It's really up to you. All these companies are reputable (even IBM to some extent). I have a Seagate Baracuda IV and it's great. However, I am a Maxtor fan. They have been the most reliable in my experiences. I had 2 hard drives on the same computer, a Maxtor and a Fujitsu. The maxtor was in there 3 years prior to the placement of the second hard drive. The computer suffers a lot of punishment when I get angry. The maxtor survived while the fujitsu needed to be RMAed TWICE. It failed the third time in another computer and I'm not going to even bother sending it in. When I got my seagate, there wasn't too many good Maxtor 7200rpm choices around. Now there is and I will definately get those in my next systems (used them in computers I built for friends). They are nice; not too quiet though, not too loud, decent speeds, overall good. I generally favor Maxtor for its durability as shown in my maxtor vs. fujitsu example.
But then again, it's up to you. Try to find a nice price and go with that one (Just make sure it's Maxtor, Seagate, WD,). Unless of course you are looking for certain attributes (noise = Seagate, speed = WD [although you won't be able to tell probably]).
EDIT: btw, I had a IBM fail on me.