these are "commodity" items, virtually interchangeable without noticing any differnce.
buy the less expensive one.
It so happens that I've seen lower pricing recently on the WD at ZZF, but the daily situation is fluid and changes fast.
I have WD & Maxtor HDDs, all the same really. Paid a pretty penny extra for the WD Raptors, can't really tell any difference in terms of human-perception. For for the best bargain price, disregard any worry over brand name, and favorably weigh longer warranty.
There look to be some good buys at this moment (changes daily) on those WD Caviars, see for instance ZZF item 101220-12 for $68.50 w/ free shipping (internal, although you said external). Good deal. Opinion merely.