Currently there are no USB drivers for Mac, and no TB drivers for Windows. Who knows if that will change in the future, or if the USB Apollos will get a similar expandability feature down the line.
All we can say is TB versions can do that on Mac, so that's your surest bet.
Technically TB is faster than USB3 (or, wider bandwidth) and there are some technical reasons why TB is an easier protocol to work with audio streams, but I think USB3 improved on some of the limitations that USB2 has, not just in speed... So again, that might not really be the case now.
BUT:
I think an important point here is that latency is something you shouldn't really need to think about with Apollo; The way Apollo works is monitoring your inputs on the hardware (with plugins running on the hardware) so you hear it back before it passes through the native buffer. So you can leave your DAW buffer size at it's max setting and still hear no latency what-so-ever when tracking, because you're not monitoring from the DAW: Apollo is doing that at the hardware. (and I do this every day)
The only case where you'd need to lower your buffer setting is when recording midi input to a virtual instrument where the sound is originating in the DAW. That is the only case where latency needs to be considered.
And in that case, the difference in latency between the TB Apollo and USB Apollo is surely much less than the buffer size of the DAW.
So if you don't record with virtual instruments, latency doesn't matter.
And if you do record with virtual instruments, the difference between USB and TB Apollo probably doesn't matter. Though you might be better served by checking out interfaces by Apogee or RME which claim to have lower total system latency than Apollo, and it matters in their case since they don't have onboard, pre-buffer monitoring.
In either case, if you can actually hear latency of less than 2ms while playing a virtual instrument with a midi controler... well, it's not possible for a human, so my bottom line is:
Latency doesn't matter with Apollo.