USB2 and Firewire 400 are about the same. Firewire 400 has sustained transfer, and uses it's own hardware control. USB2 is burst-based transfer and pulls on the computer CPU. USB2 tends to be cheaper to implement than Firewire 400, for this reason. There's nothing wrong with USB2 for more uses -- excluding DV video transfer "capture" (firewire required for DV, as it requires a sustained speed connection).
Firewire 800 is faster. Again, sustained and relies on its own hardware controller. This tends to be a Mac-only format, for the most part. You don't see it on Windows machines too much.
eSATA is best of all. But you don't often see this on Macs, only Windows and Linux machines.
I have a RAID-1 drive that can use USB2, Firewire 400, Firewire 800 and eSATA. But that's a very unusual drive. You generally have to pick your transfer type. Most of my drives are USB2 drives, although I also have a few eSATA/USB2 drives (mostly connected via USB2, because I have more USB2 ports than eSATA ones).
All of these will work for you.
For large galleries full of RAW images, you'll want to look into using Lightroom as the DAM (digital asset manager), and then Firewire 800 or eSATA is my suggestion for optimal drive configuration. RAID-1 if you can afford it, to get mirror backup.
Be sure to read this: http://www.digitalFAQ.com/forum/show...rive-2189.html
If budget is tight, a good Western Digital USB2 will be fine. Consider a WD MyBook 1TB drive Firewire/USB drive for about $140.