I've worked as a PC tech for over 14 years, ever since that beauty Windows 95 replaced Win 3.1.
I was a fan of IBM IDE until they started failing and sold to Hitachi. And the first Hitachi IDE drives were as reliable as a crack whore, so ...don't what they 're like nowadays. I will tell you that Dell Poweredge Servers use Hitachi SAS drives and the failure rate on those, under constant daily use, is minimal.
Years ago, Maxtor Atlas SCSI were great drives, if not a little noisy (crunchy), but I loved 'em and they were very reliable. I'm sure that when Seagate bought Maxtor, they learned a thing a two.
When it come to desktop drive reliability, regardless of the brand, who knows what your gonna get. I've seen DOA, dead in three days, dead in 30 days, dead in a year, and I've also seen some old drives that just keep working forever. Seriously, I have a couple 8 GB maxtors and western digitals around here somewhere that still work fine, if not relatively slow, but that's bc they are older technology (UDMA 33, etc), but they work and they're over 10 years old for Christ's sake.
And as far as failed drives in PCs, it's about the same for WD and Seagate: either one will fail, with maybe a slight edge towards WD Black drives, but I couldn't prove it.
Currently, I like Seagate, mostly because of the warranty, and the simple RMA process. (Although WD is now offering a 5 year warranty too) Yeah they started charging for fast shipping and advance replacement, but I select the 'free' replacement options. I just replace the drive with a new one in the meantime, and when the RMA drive comes back I keep it until I get a chance to put it in another PC. (and yes, even if the drive is a week old, you WILL get a 'reconditioned' drive as a replacement).
I'm sure you've all read about Seagate fiasco with their 500 GB drives, but that's hopefully not going to happen again. I don't have empirical data to back this up, but I think their 160/250/320 drives were some of the most reliable ever made. Something happened in the jump to 500+, and that goes for all brands.
Ironically, the least reliable disks I've seen are external USB drives, which most people use as a backup. I have seen people have an internal drive fail, and then the backup drive immediately fail when they go to recover their stuff. The backup seemed to be working, but when asked to actually do some work (ie, transfer 500-1000 GB of data) they crap out. I believe it is because people think they can move and knock those drives around while they are operating, and that's a no-no. Never move or bump an external drive while it's operating, no matter what kind of BS it says on the package. Turn it off and wait 30 seconds until it has had time to spin down and park.
The big difference is going to be when you go from a desktop drive to a server drive. (BTW, SATA is not server class, just cuz it came in a server doesn't make it a server drive). I'm talking SCSI or SAS. My desktop/workstation has a pair of 36 GB 15k RPM Cheetahs (Seagate) in a RAID 1 that have been running daily for over 8 years now. ( Cheetahs rock!)
Servers with SAS drives have very little, if any failure (that doesn't mean you don't have to back up). And yet, I also have a RAID 10 array with 4 drives (7200 RPM Seagate 500 GB) that has none of the original drives left, all the drives have been replaced at least once since I built that array 18 months ago.
Without a doubt, SCSI and SAS drives are more reliable than SATA or IDE, but occasionally one of those will fail too, just much less frequently.
I have been installing Western Digital Velociraptors (SATA) on desktops for power users and using them in RAID arrays for servers since they came out, and I haven't had a single one fail yet. They are pricey, but they are very responsive and seem to be very reliable so far.
Fujitsu, no longer making drives.
Samsung...make great phones, but I haven't seen enough of their hard drives to comment. They seem do be doing well on Newegg, though.
So, in summary, the reliability spectrum:
External USB < TB+ desktop SATA < Under TB SATA < under 500 GB Desktop IDE < Seagate/Hitachi SCSI or SAS/ WD Velociraptor (tie for first).
my .02c