The Western Digital WD1200JB and WD100JB (the drives with 8Mb cache) are noticeably faster than anything Maxtor offers in bootup, loading game levels, and even browsing the web...as confirmed by the real world bootup and gaming tests on Storagereview.com. Other than the two drives with 8Mb cache optimized for desktop apps and games, Western Digital doesn't have much going for itself. In sizes smaller than 100Gb, Maxtor's drives are better/faster than the WD drives; because they are available in smaller sizes, the Maxtor drives also tend to be cheaper (although there were some great deals recently, like the WD1200JB for $177 shipped from Dell two weeks ago).
Also, if noise is an issue, all the high performance WD drives produce more noise than the Maxtor drives...although the Maxtor drives, even in the fluid bearing model, are nowhere near as quiet as the Seagate Barracuda IV.
The latest drives of WD, Seagate, and Maxtor are all roughly equal in reliability.