Approximately 4 years ago, I rebuilt my DAW, and shortly thereafter I decided to punt the whole internal soundcard paradigm to the curb and switch over to a Firewire-based external audio interface. This brought with it a couple of advantages.
For one, I don’t have to screw around inside the case to install a new interface, nor do I have to deal with some complicated dongle or breakout box to handle a large number of inputs and outputs. Along those lines, it also worked wonders on the maze of spaghetti vomited out the back of my PC.
Second, there is less of a configuration headache during the install because I do not have to rummage around for a PCI slot on my board that has dedicated resources. In the past, some of the difficulties I’ve had with this (which can result in high latencies and instability) have been nearly insurmountable (see the Oasys PCI and Yamaha SW1000SG).

Up first: TC Electronic Studio Konnect 48

When switching from the previously mentioned combo of an Oasys and SW1000, I wanted an interface with low latency (making ASIO drivers a must), flexible routing, expandability, high quality preamps, and since I planned on still using the Oasys occasionally from a separate, dedicated system, ADAT I/O. After deliberating a while, I finally chose a TC Electronic Studio Konnect 48.
At the time, this was a new product with questionable drivers, so I knew I was taking a bit of a gamble, especially at the $1199 price. But the most recent reviews of it said that the software had come a long way (and was still being actively worked on), the hardware was brilliant, and in general it was shaping up to be a great interface.
However, the things that really sold me on it were the I/O and expansion options. I came with 4 high-quality preamps, 8 analog line inputs, 8 analog line outputs (in addition to the main stereo outs and dual headphone outs), 2x ADAT I/O, S/PDIF in and out, MIDI, and wordclock. 
Further, it is built with expandability in mind, and you can chain two units together and control them as a single unit.
Finally, it also comes with a great little remote unit that operates as a volume/effects control, talkback mic, and even guitar tuner.
So, how did I like it? Well, first, let me say that I kept it for roughly 3 years, which is a testament in and of itself. Ultimately, there are a lot of things to like about it.
First, the build quality on the unit is impeccable. It looks gorgeous, and ‘feels’ high-end. all of the knobs and buttons, connectors, dials, etc. all feel and look like top of the line items.
Second, it sounds awesome. The built-in preamps, to my ears, are clear and transparent. There is also enough gain in the stock preamps to support an SM-57, though just barely (I ended up purchasing a Golden Age Pre-73 to drive my SM57 with more gain, but the difference is not huge). Additionally, all of the preamps support a 20 db pad and phantom power, which is also a nice touch. 
Third, the DSP-based effects are really stunning. Not only do they sound great, the novel approach to configuring them causes you to think differently about the sound you are creating, which is great. Also, everything (including the software) has a very appealing appearance. I’m not big into aesthetics, but it does help with first impressions.
However, despite my overall satisfaction with the unit, there are a few warts that I encountered and that ultimately helped push me into the Saffire.
First and foremost, the software (specifically, the drivers) leave something to be desired. In their present state (2.5.1 as of this writing), they might actually be pretty good, but the last version I used was 2.4.1.6489, and my gripes are largely present in this version.
The biggest problem I had with the drivers was getting good latency when using Sonar. Now, mind you, this doesn’t mean I couldn’t get low latency, just that it was difficult. I spent hours troubleshooting the config to nail down one that would run stably in most projects.
While this may not seem like a big deal, keep in mind that I’m already running on a system that is purpose built for audio. Specifically, it has a Texas Instruments firewire chipset, and is running a dual-boot Windows 7 x64 config, where the ‘DAW’ boot is completely clean and optimized for audio. Furthermore, I went to the additional step of completely disconnecting the Wi-Fi adapter from the system and disabling all networking drivers in the DAW boot, to further reduce DPC latency.
And yet, despite all of this effort, the interface was still frustratingly fickle. Ultimately, I ended up setting on sub-optimal latency settings (24.7ms or higher round-trip) just to make sure that I didn’t get a ton of random drop-outs when the load got heavy. And high latency settings make it almost impossible to record.
Furthermore, the interface drivers caused general system instability in my DAW, and would cause random (though rare) BSODs. While the BSODs were not predictable, they were reliable. In other words, I could not predict when they were going to happen, but I could predict with 100% certainty that if I left the interface running for long enough (24 hours was usually enough time), it would BSOD. Also, while they were rare, they were unpredictable, so every time I fired up the interface I got a little nervous about it. All it takes is losing a few hours of work on a project due to a random BSOD to foster a little paranoia, and paranoia is not something you want to be feeling while trying to create art.
The final software issue I want to hit on is the inflexibility of the I/O routing in TC Near, which only became wholly apparent when I began micing my drums, and is ultimately the main reason I switched interfaces.
You see, the main reason I miced my drums was not to record them. By and large, I don’t record drum tracks on real drums, I do it electronically. However, when practicing, I much prefer to play real drums, and my favorite way to get general practice in is to play along with music. However, this leads to it’s own problems.
For starters, to play along with the music, I use sound isolating headphones (previously Sennheiser HD-280 PRO headphones, but currently CAD Audio DH100 Drummer Isolation Headphones). These are both great at blocking out the drums and allowing me to hear the music, but the problem is, they both block out too much of certain frequencies. This makes it harder to hear certain hits (namely, cymbals and bass drum), which causes me to hit these harder. Since I already hit hard, hitting harder doesn’t actually produce much more sound, but completely destroys my equipment, and I started going through cymbals like crazy (I broke a china in less than a month, for example). So, in an attempt to combat this, I decided to mic my drums and adjust levels as necessary.
Unfortunately, TC Near doesn’t provide a way to directly monitor inputs and control the level of sound output from Windows simultaneously. Basically, if you enable low-latency monitoring in TC Near, you cannot hear the media player through the interface. However, if you disable monitoring, you cannot hear your inputs. My only option was to load up Sonar, create a project specifically for practicing, and route I/O there, which meant living with the ~30ms ASIO latency while practicing. It also meant a fairly involved amount of prep just to practice.
Other than the software issues, I did have one hardware failure in the unit approximately two years post purchase where it simply stopped working. I emailed and called TC’s North America support, and was told that out of warranty repair was a flat $125 fee regardless of what was wrong with it, which is an absolute steal. I sent it in, and while it took over 3 months (and another phone call, because apparently they forgot about my ticket) to resolve, the resolution was a brand new unit shipped to my door for $125, which I thought was highly satisfactory.

Choosing a new interface

Still, all of this would have been OK, but it also turned out that 4 preamps is just insufficient when you want to control levels on each individual drum. To mic my whole (small) kit, I need a minimum of 7 preamps, which meant I needed to buy more gear.
Truthfully, all I needed was a bunch of preamps, so I started looking at my options. The most attractive one was a Focusrite OctoPre MKII, primarily because it can both run at 96Khz and output to ADAT for routing back to the audio interface. However, at $500, it’s a little steep compared to a Behringer ADA8000 at sub-$200. However, while looking for preamps, I noticed that the Focusrite Saffire Pro 40 was only $440, and it already had 8 preamps. This looked like the deal of the century, so I dug in further and, after some research, bought it.

Focusrite Saffire Pro 40

First, the selling points that hooked me on the Saffire were:

• 8 Preamps
• Similar I/O to the Studio Konnect
• Promised flexible routing in software
• Possibly better latency
• Almost guaranteed better stability
• Price

Let me start off by tackling each of these in turn.
First, it includes 8 honest-to-God preamps and a ton of additional I/O, with wordclock and a second ADAT port being the only major missing parts. To my ear, the preamps sound reasonably clean, though I’m not sure they have as much gain as the TC preamps. Also, only two of the preamps have pads, which is kind of a bummer considering what I am using them for. However, to compare, I recorded my son Tylor playing a short snippet on an acoustic guitar through both interfaces. Both were recorded at 96k, 24-bit, and both are completely bare (no processing). The left channel is taken from a Nady SP-1 placed at the neck of the guitar, and the right channel is a Shure SM-57 placed at the soundport.

Audio Samples (WARNING: 25 MB Wave Files Each)
TC Electronic
Focusrite
NOTE: There are some slight pops at the end of the Focusrite recording, but that is totally due to me getting a little too aggressive with the latency while recording it, not noise in the interface.
For routing, it works as advertised, and I think you can route just about anything to anything. I had absolutely no problem setting up a routing arrangement that allows me to hear all of my inputs while listening to and controlling the levels of my audio player output. In fact, I just recently had a hearing test which showed that my right ear is ~20db off from my left ear. The routing in the Saffire is so adjustable, I was able to easily configure two identical mixes, hard pan them right and left respectively, and reduce the gain on the left channel to compensate for my bad right ear.
On the latency front, the Focusrite delivered there as well, but not by a large margin. In my non-DAW boot (high DPC latency), I was able to get a stable round-trip latency of 18.7ms under load (10 mono audio tracks with compression and EQ plugins) on the Focusrite. This was using ‘Medium’ driver stability settings at 96khz with a 480 sample buffer size.
For comparison, in this same boot, I was able to get a 19.4ms latency from the TC (96k, Safe Mode 1, 512 samples); However, this was in a blank Sonar project (1 stereo audio track, no effects). In reality, I am lucky to get 24.7ms latency on the TC stably when booted into the DAW-specific partition under load.
The reason the conditions are not the same is because the TC is so much more fickle about the environment. This makes it very difficult to get good latency settings without booting into a completely clean OS, while the Focusrite had no such issues. So ultimately, the latency itself isn’t that much better on the Focusrite, but the stability is so much higher that I can use the interface in situations where the TC simply wouldn’t perform at all.
Speaking of stability, the Focusrite has been rock solid since hooked into my system. I have had zero issues with it, and that includes a 72-hour long burn-in period. I have not seen a BSOD since removing the TC.
Finally, the price of the Focusrite is unbelievable. In fact, for me, it was basically free. After spending two weeks with it and deciding to keep it, I put my TC up on ebay. It sold for $600 within a few days, more than paying for the Focusrite.
In short, I’m happier with the Focusrite mostly due to software. That being said, I do miss some features of the TC, such as the awesome tuner and great effects. It’s kind of depressing that TC can get so much right and still go so horribly wrong, but ultimately, the promise of the interface doesn’t make up for the day-to-day headache.