Mark is looking for a 2TB desktop hard drive. Leo says that hard drives are commodities these days, and no one brand is really better than another. Leo does use Western Digital though, the Caviar line. They're 7200 rpm and he can get them in various models. "Red" drives are for network attached storage and are slow, but reliable, "Black" drives are faster and "Green" drives are eco-friendly and lower power. The VelociRaptor models are 10,000 rpm and are great high performance drives. But now that we're in the world of SSDs, spinning hard drives are less important. He should avoid hybrid drives though. Leo says those are the worst of both worlds.
The chatroom says that BackBlaze did an article on what hard drive you should use, and they buy a lot of them.