I have two Western Digital powered USB drives (that's the 2TB and one of the 1TB's), and one portable (USB-powered) Seagate 1TB.
I also used to have a Maxtor 500GB, but it just stopped working one day.
Now, the reason I have the portable one is my Seagate FreeAgent Theater+, which is a thing that plugs into your TV, that you put a hard drive into, and you can watch almost anything (including 1080p MKVs, in 1080p, with Dolby or DTS 5.1 and all that). It has two USB ports, plus a slot on top that fits a Seagate portable hard drive. Hence, my owning a Seagate portable hard drive.
To be honest, I love the portable one so much that I almost never unplug the other two. The WD 1TB holds all my movies, and the Seagate portable 1TB holds all my TV shows (I put those on the portable since I watch them more often), but it's so much easier to use the portable that I just copy whatever movie I want to watch from the WD to the Seagate whenever I want to watch it.
So, my recommendations:
- Western Digital is always good
- Seagate's not bad
- Don't get Maxtor
- Portable HDs are great if you know you're going to be going back and forth with it a lot, HOWEVER I have noticed that if I try to HandBrake something directly to the portable, it has about a 98% chance of failing. I have to HandBrake it to the desktop, then copy it to the portable.
- USB is decent unless you know you need something faster, in which case I'd recommend FireWire.