I’ve got a 320gb and a 1tb Seagate Expansion Portable drives. Not had any problems with them, had the small one for a year and the big one 6 months.
Use the 320gb as a time machine backup on the mac, and the 1tb one for storing my dvds and old iTunes downloads, so neither gets really frequent use.
I read some worrying reviews about the power needed to power the big ones; suggesting you need a double USB cable to power it. I’ve not found that I do, and it actually doesn’t mount with the double cable that I use for the external DVD player.