Ideally all of them. I'm doing a film program this summer for which a Firewire drive is recommended, but afterwards, I'll be using it with a MacBook, a Retina MBP and a Late 2012 iMac, so Thunderbolt, USB 3 & USB 2 would also be great.
There aren't many firewire drives left. Looking at the Apple store, there's a couple Firewire/USB, a few more USB/Thunderbolt, but I didn't see any TB/Firewire.
Drives that support USB 3.0 are backwards compatible with USB 2.0 - and you'll pay a lot less for one that's USB only.