Here's another discussion that may be interesting to the posters here to browse over morning coffee. This over 3 year old thread is still alive.
 
 
Evaluating AD/DA loops by means of Audio Diffmaker
 

John T

Jim Roseberry
Anyone who thinks that a top-notch USB2 audio interface isn't up-to-snuff for professional use is simply wrong. 

Quoted for truth. USB2 is, practically speaking, just as fast as Firewire 800.

Sorry, it isn't so true... What does it mean practically speaking? Firewire 800 is surely much faster, solid, software independent than the poor USB2.
Look at this article (I don't use Apple, I use PCs, but the article is well done)

I've done the same trials on PC and there are only facts. If you want a professional, serious interface, the only choice is Firewire.
I've tried USB interfaces, but the problem is that when a system gets to a heavy load, the USB fails. The FW no.
If you have a very, very powerful system probably you don't notice the difference, but with USB you always must reserve about a 20/25% of pc power only to let USB work correctly.
Probably the USB is easier to configure, but once you have a FW device connected and working, your work is rock-solid!
Cheers

LunaTech
Hello,
 
I agree with the statement that Firewire is not as popular.  It is still however,  a viable choice.  As with most technology, its honeymoon is short but its usefulness is unique to individual preference and how long it is used. 
 
On a different note, I use the Zed R16 mixer. It has the firewire interface. It is an impressive piece of equipment with more than respectable conversion, excellent preamps, highly useful eq, analog summing capability and great build quality.  I would personally compare it to some of the best names out there (Not calling out anyone in particular) in overall sound performance ... dollar for dollar value without reservation. I think it is one of the best buys out there. A different approach to an interface , been around a bit (2008) but highly effective, versatile and useful... My two pence.....

Oldish thread resurrected I know but I can "+many" on this. I would buy another one tomorrow in the unlikely event it suddenly stopped working. Actually I'd probably buy it's bigger brother the GS-R24M but the ZED-R16 is awesome especially if OTB mixing is your bag.
 
Might be a bit overkill for some but if you want total routing control with great Pres, fabulous EQ, then the ZED is it.