Normally don't post on SD. But I felt I need to add some input here.
From personal experience, I have had some good luck with WD Drives.
But I also own quite a few seagates that i purchased for a small server build a few years ago.
I have 4 diff computers that run WD Greens and also Blacks, the oldest ones being about 3-4 years old now which is are 1TB Blacks (still ticking away) and no issues. I also have 4x 2TB drives in one system in a raid set-up and none have failed (WD Greens). They have been reused in 2 diff systems now and still no issues.
My Home Server houses 6x Seagate Barracuda LP, all 2TB in a raid array, while I didn't have any issues for a long time these drives are about 3-4 years old now. I recently had 2 die no power, lucky it was in a raid and I was able to stick 2 of the newer seagate 2TB drives in and the array rebuilt with no issues. While the dead drives showed no signs of failure before they went it was a little bit of a headache for me.
I do have 2 WD Reds in a 2 bay Dlink NAS, they seem to be working fine, but notice that the data transfer is a bit slower. But that can be caused by lots of things and not the drives directly.
While there isn't a def. scientific way of measuring failures of the drives at this time (at least here on SD). Drives are all mechanical. One way of another they will fail eventually. The thing you should be looking at is warranty. Lucky for me at the time I purchased my seagates, they still had the 5 year warranty. So I sent mine in recently, but one thing I don't like about seagate is that they return a refurbish drive to you instead of a new drive which in my book is a big no no, I hate using refurbish drives since I have no known knowledge of what happen to this drive previously.
WD on the other hand, returns a new drive to you during RMA (at least the last time I had to RMA a WD drive)
At the end of the day, the best way to protect your data is to back it up. I do a monthly back up of all my data. At least the important stuff that is not replaceable. So all and all, both brands will have reputation of failed drives. Also in retro spec, there are allot of users that will never post good things and type reviews. The ones that hit the net more often tend to be the bad reviews since the user is upset and want to vent about the experience, one way or another. so we tend to hear the bad more then the good. just my opinion.
Just RMA'd a WD Red within the last 2 weeks, they send you back a "recertified" drive, not new.