In terms of 3.5" external drives, I've got a Western Digital My Book and 2x Seagate Expansion Drives and 1x Seagate Backup Plus.
The first My Book I had crapped out on me, but it was the enclosure that failed. Without the same enclosure, or at least the same bridge chip, I was unable to access the data on the actual drive. Since I don't make use of drive encryption, that feature is more of a hinderance than a benefit.
Having said that, I suppose WD drives are more reliable, but Seagate hasn't given me any more trouble than WD has over the years. Both are good drives in my opinion. I usually just go with whichever is cheaper at any given time.