Interesting thread, as all the hard drives I have in my systems are either Samsung or Western Digital drives.
Score on the board for failues so far:
WD 2 : Samsung 1
Thats out of about 10 drives. I must point out that the Samsung failure was even my own fault (plugged it into a Hotswap bay that was killing hard drives electrically).
What I can say though is both RMA services are very good - Samsung even turned around my replacement drive same day it arrived, for a total of a 3 day turn around! Western Digital are more like 5-6 days.
It horses for courses I guess. I'm buying my next batch of 4x 500GB drives at the end of the month, and I'll be picking up the Samsung F3's...