Darren Ashby, via email
SOS Editor In Chief Paul White replies:
After speaking with various interface designers, it seems that both USB 2 and Firewire 400/800 are equally capable of handling in excess of 16 channels of simultaneous audio (which, of course, would be well over the top for your current needs), while USB 3 is considerably faster than Firewire and can handle a huge channel count. However, USB 3 audio interfaces are not yet widely available, and the only model I know of to date comes from RME, who use field-programmable gate arrays (FPGAs) to create, in effect, their own USB 3 equivalent.
You may have noticed that many current computers come without Firewire and it is generally accepted that it is being phased out, while USB seems to set to continue for a good while yet. So, in terms of future-proofing, USB 2 seems a safer bet than Firewire. Having said that, reports suggest that Firewire interfaces work fine via an adaptor cable when connected to the Thunderbolt port on a modern Mac, so it doesn't look like those Firewire interfaces will have to be thrown in a skip anytime soon.
In your situation, with not a huge budget and relatively small track counts, I'd be inclined to go for the USB option. But make sure you plug the interface into its own USB port and not via a hub, to ensure you have enough bandwidth for it to work properly.
As for Thunderbolt, these interfaces are still relatively expensive, but will no doubt become less so as more products enter the market. However, it doesn't sound as though you need to take this step right now. It might seem logical to assume that Thunderbolt interfaces are the least likely to become defunct, as they're newer technology, but I'm afraid the only thing you can be really certain of in the world of computers is 'change'.