I recently ran through a Seagate and now have a WD. Just to note, the drives are fine, stupid mobo has defective SATA channels so I had to get a WD IDE HDD. Anyways, the Seagate was MUCH quieter, and I never even heard anything from it (i.e. head parking, spinning, etc.). The WD however is louder with a click on boot and shut down from the head park, which scared the crap out of me when I first had it; apparently, it's classified by WD as normal. In terms of reliability, I've had the WD for about 2 months now with no problem. The Seagate is running in another system fine for 4 months. I actually wanted another Seagate, but they only had 80Gb IDE with 2 Mb cache so that was a no go. Oh well, I'd go either way with WD or Seagate now.
Check out WD's site on warranties. Their "retail" drives only carry 1 year while OEMs go for 3, and if you want it extended to 3, gotta pay up. May be better off going OEM and saving a few bucks there. Think Seagate has 5 year so that's a bit better.