I was in this dilemma, although I think the firewire mixers are better than the usb mixers. I've decided on a mackie 1220i, understand the limitations versus the 1640i (16x2 firewire instead of 16x16, which means it can only return 2 channels back to the mixer from the computer via firewire instead of 16). But my needs are very specific, I needed aux routing to external effects, and I also needed a mixer for live use anyway, so it just made sense. Yes you can do aux routing with an interface, but its a lot more complicated in my mind, plus this way my studio setup and live setup will be streamlined.
On top of that, I don't currently own a mac, and am on a budget, so motu ultralite and RME interfaces are out of the question. Makes a lot more sense for me to go with the mackie now, and an RME or motu ultralite down the road when I get more serious about recording and actually own a macbook pro. Right now I just want to record jams, essentially rehearsals for live sets.
Also my setup is hardware-based electronic instruments and bass guitar. If I used my computer or software as an instrument, obviously I would need an interface.
Mackie 820i: $450
Mackie 1220i: $600
Mackie 1620i: $1000
Mackie 1640i: $1600
Only the 1640i allows for analog mixing and summing because it can return 16 channels from the computer.
I understand how nice the Presonus StudioLive boards are, but if we're strictly talking recording, I would still take the Mackie 1640i over the StudioLive 16.4.2, and the A&H Zed R16 over the SL 24.4.2, simply because analog summing makes a huge difference to my ears.
Hope this helped.
Edit: Also, the Mackie 1640i is not that much more than the PreSonus 16.0.2, and is rock solid on a Mac, I have some friends who run a studio/venue hybrid out of their basement with that setup. I can also tell you from reading the PreSonus boards that the 16.0.2 has been giving Mac users huge headaches when it comes to recording via firewire. Multiple users experiencing the same issues with recording, with no solution in sight. It seems mostly to do with OS X Lion. So to the dude looking at the SL 16.0.2: Spring for the Mackie 1640i, especially if you have a Mac.