I have both the 8MB 80GB WD 800JB and the 8MB 80GB Maxtor Diamondmax + 9. They are both great drives. The WD is slightly faster and has a faster access time. The WD is also totally silent (seeks and idle), whereas the Maxtor is silent at idle but it has very faint muted rumble seeks, still very quiet and definitely not a problem, but if you want total silence and best performance, in my opinion the WD is the way to go.
If you are on a really tight budget, compare the prices and take the cheaper one, since both are fast, excellent drives. No one can give you info about reliability since both are relatively new drives, but the WD is older and there are at least no big reliability issues with it. The Maxtor is certainly too new to tell anything.