Your only concern for looking at a higher grade drive is if you plan on leaving your drive hooked up and running 24/7. The highest speed USB chipset on the market right now is the Cypress CY68300B chipset. You might look for an enclosure using that.
I posted links to a couple of external drives awhile back that others are having good success with. I have not been able to make my Seagate DB35.3 choke yet but typically the usb chipset will be your biggest bottleneck.
For those who are turning their drives off most of the time, MyBooks and FreeAgents are working fine.
But it is early yet!
I've been searching for an enclosure that uses the CY68300B chipset but have been unsuccessful thus far. Are you aware of any?