Seagate Barracudas get the

from me. Fluid bearing, thus really quiet. I've got a Mac G4 MDD, the loudest machine they ever made, and I quieted it way down with fan replacements. But replacing the stock HD with a Barracuda put the final smack down on the whining noise problem. You can barely hear them spin up, they're very polite.
My PC's drive crashed a few months ago. I got a quote from Drivesavers on what it would cost for emergency surgery: Between
$500 and
$2700 for a 120GB drive!!! No kidding! If that isn't enough to scare you into backing up your data I dunno what is. I lost my system disk but still have all the data stuff on another drive.
SCSI is probably more reliable. I've been flirtin' with disaster with a 4-drive RAID-0 array for seven years and counting. It was the IDE drive that failed, though. I guess you get what you pay for.