I don't think it matters between the 8MB drives, let price be your determining factor. I've gotten as good if not better deals on my Maxtor Ultras (through Raples) as any of the WD's, so keep your eye out and be ready to jump on a deal when you see it.
But if you absolutely MUST have the fastest drive, even if unnoticeable, for the sake of peace of mind, I would wait for the full reviews pitting the WD SE's vs the Maxtor Ultras. Early tests indicate that the Maxtor Ultras will be the fastest of the 8MB cache IDE drives b/c of their 80GB platters. Digit-Life had a review of the 5400rpm and 7200rpm 2MB cache Maxtors with 80GB platters and both performed almost as well as the WD SE. Shockingly, the 5400rpm drive performed better than both the 7200rpm drives in a few important tests. You can check out the review at Digit-Life; They also said they are working on a full comparison between the 2MB vs. 8MB drives from both WD and Maxtor, but judging from the results its pretty clear who the speed king will be.
Chiz