I know it is only anecdotal, but I have mostly WD drives (all mechanical), as I have had the best experience with them, and had bad luck with Seagate in particular.
I have a 320GB and a 500GB(ish?) external WD. Both have been hauled around in a laptop bag on airplanes and helicopters for years. Still work great. Have much newer 1.5TG and 2TB WD externals which have done the same, but not as long. I have (desktop external) 320GB, 750GB, 2TB and 4TB WD models (you can kind of guess the ages by the sizes) all still working away.
I had picked up a Seagate external (1 TB or 1.5TB I think) and it died in less than a year.
Wife's laptop internal (Seagate) drive just failed in less than a year (warranty still good, yay!).
My laptop internal failed recently as well (Toshiba), about 2 months past the 3 year warranty.
At work we had a desktop external Seagate drive also last less than a year.
So I am a small sample size, but anecdotally, my experience is:
- Eight WD drives working fine
- Experience with 3 seagate drives lasting less than a year (2 owned, 1 at work)
- One Toshiba drive lasting 3 years