Despite what chscag said, I really don't think it matters. I do prefer to spend my money on companies that make drives that are pre-formatted for Mac (and particularly those that include Firewire, since it's faster than USB2), but hard drives are kind of like light bulbs: they SHOULD work reliably for years, but they COULD fail at *any* moment, and you generally don't get a lot of warning when they do.
I have two "computer" backup drives, a Misc. Media drive and another drive to back THAT up. The two older drives are both WD, the media drive is Iomega, the media backup is Hitachi. All work perfectly well and have done for years. My replacement internal drive is a Western Digital as well.