Both companies are troopers. The answer is difficult.

Like someone else mentioned the Maxtor D740X was a great HD. I would recommend checking which one can hold more data per platter and that is probably the more faster one. If they're both the same then you're in a pickle.

I would recommend the Maxtor HD for your rig because your mobo can take advantage of the ATA133.
I understand that the boost from ATA100 to 133 is very like, like 3-6% but hey it's something.

Both comanies have under 1% deffective rate on their HDs according to them. So reliability on the HD not breaking down on you is pretty much the same.
Both are OEM, so the warranty is the same for both....

Maxtor vote here because:
Slightly cheaper
ATA133
I've personally had more WD hds break down on me than maxtor, but like I said earlier, the HD breaking down is relatively the same for both companies. You will find other people with more maxtor HDs breaking down than HD.

A tie, but because of the above reason I lean towards the Maxtor HD.