Don't worry about firewire being phased out as a connection on the Mobo. Most people use a PCI card anyway. This is the better option since you can match the card's chipset to your interface.

Rme has some usb 3 interfaces . I tried the second focusrite you mentioned for a month. I adored the sound but had fire wire issues in my laptop. Ti card. So I returned it and eventually got the rme. The rme is cool and is more transparent than the focusrite, but do love it and use the related software ALL THE Time. I watch TV monitoring the spectral analyzer et al. My Ucx is not a usb three device, but it has usb3 drivers and works fine on usb3 ports.

When say more transparent I mean it didn't have the liquid pres . Those liquid Pres are awesome.

I originally wanted to go with the Saffire Pro and FireWire. A whole slew of folks talked me out of it, mainly because there is such a pullback from firewire these days) and I went with the Scarlett 18i6. It's been flawless.

I have two units now (since I have a laptop). One is tethered to all of my 18 inputs and 6 outputs in my studio. The other one I carry freely around with me when I pick up my laptop and work in another room or location.

Sounds great and easy to use.

You won't notice a difference in performance between a USB2 audio interface vs. Firewire.
The best USB2 units offer low round-trip latency... right on par (a little better in some cases) than the best Firewire units.
ie:  The RME units yield 4.9ms total round-trip latency at a 48-sample ASIO buffer size/44.1k
 
You previously asked about the FastTrack Ultra 8R.
That unit is actually pretty decent.
I shelved mine for a good while (when they removed "high-performance" mode - which offers low round-trip latency).
With the latest driver update (recent), high-performance mode is now back.
Round-trip latency is 5ms at a 64-sample ASIO buffer size/44.1k.
The analog section is just a little bit bright (compared to some units), but you can capture good results with it.
If you can source one for under $300, I'd definitely consider it.
I used mine playing soft-synths live (64-sample ASIO buffer size/44.1k) using Forte' as a host.  Never a single glitch...
 
The Focusrite units offer ever so slightly better fidelity.
The M-Audio unit offers lower round-trip latency.
 
If you go with a new Focusrite unit, I'd opt for USB2 over Firewire.
Firewire isn't going to immediately disappear... but it's nowhere near as common as USB2.
Again, there's no performance gain going with Firewire, so you may as well get the unit with the longest shelf-life.
 
If you get a Firewire unit, you'll want to use a PCIe TI chipset Firewire controller.
That eliminates most compatibility issues... and ensures maximum performance.
Certain Firewire units are *very* particular/finicky about the specific TI chipset controller (ie: Mackie and Tascam).  

As Jim et al says above, FW will be around on pci cards etc. but USB will be native.  Thunderbolt seems like thunderdud w/ the slow adoption rate, except on Macs.  Maybe if they lower the price?  $500 is more than a lot of computers these days.
 
But USB is fine for most jobs, USB 2 is fast enough for most recording, so I would go that way.  A bit safer, esp. if you plan on keeping the interface for a few years.
 
@

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As Jim et al says above, FW will be around on pci cards etc. but USB will be native.  Thunderbolt seems like thunderdud w/ the slow adoption rate, except on Macs.  Maybe if they lower the price?  $500 is more than a lot of computers these days.
 
But USB is fine for most jobs, USB 2 is fast enough for most recording, so I would go that way.  A bit safer, esp. if you plan on keeping the interface for a few years.
 
@

Thunderbolt is great... but when it's a $500 option for your audio interface (ie: Apollo) that's a serious consideration.
 
Thunderbolt external HDs are also extremely expensive.
USB3 enclosures top out at ~550MB/Sec (fast enough for most users - a little faster than a good SATA-III SSD).
ie:  A 3TB external Thunderbolt HD is ~$350.  The USB3 version is ~$130

I was looking at the Focusrite Scarlett 18i20 also. But I read a user comparison with that and RME Fireface and though they are very close,
he said RME pre's have a more "3D" sound compared to Focusrite which sound more "2D"
 
Waiting to read some reviews on the Roland Studio capture.

Ted: go with firewire and Ti chipset card.. you will not have any issues !

Here is my two cents, since I faced the same decision a month or so ago. In the specific case between these two Focusrite products, the drivers for their firewire products were updated in May of this year, with very favorable results as far as low latency performance is concerned. The USB 18i20 is quite new, and according to some of the feedback I have seen, there are still some issues to be worked out with the drivers. You may want to check out the May '13 results on www.dawbench.com/audio-int-lowlatency.htm
 
The results on that site seem to indicate that more often than not, at least for the interfaces they tested, there was a slight advantage in low latency performance with firewire.
 
Another difference between the 18i20 and Pro 40 is that for some reason, the MixControl software for the 18i20 allows only 8 output channels instead of the 16 allowed on the Pro 40. Maybe it's because some software horsepower had to be diverted to the word-clock out, which the 18i20 has but the Pro 40 does not.
 
I chose the Pro 40. My motherboard had a TI firewire chip. I downloaded and installed the latest drivers. The Pro 40 worked perfectly right out of the box with my computer, and gives low latency performance in line with the results posted for the Pro 24 on dawbench.com, in fact, a tiny bit better. I am extremely happy with my choice.

Thanks so much folks...!!!  Some very valuable info here.
 
Jim,  I've seen a few different online sellers with the FastTrack Ultra 8R for $269 with free shipping.  That is a pretty good deal...I was just concerned about drivers, but have noticed on their website that they have fairly updated drivers...which is nice to know.
 
I like the Focusrite products simply because I like a product that has the power supply built in...ie it uses an IEC power cord plugged directly into the unit instead of using a wall wart.  Plus the fact that there are really good reviews about the preamps and included software (along with the fact that they include some Focusrite Plugins).
 
Now it's time to make a decision :) . 
 
Thanks again folks...!!!  You guys rock.