For internal disks:
Personally I had many Seagate disks in the past and only one had bad sectors but due overheating (a place other hard disk on my Seagate). I had three WD disks, one was 2Tb from black serie and it died, hopefully it's shows real signs of dying so I managed under linux restore most of my data. Now I have one Seagate SV35 and it works great for more than two years.
At work with more than 120 computers only one Seagate died totally while I had couple WD disk with bad sectors and one totally dead. All WD red disks are working fine (working in NASs all the time).
For external disks:
All disks I had (Seagate, WD or any other like pqi) failed after some time or at least shows some problems, especially USB3.0 ones.
My advise is to take some high end/more expensive disks and put in external shell rather buying ready to use external one. Please note that WD external disks are usually green ones (cheapest) and Seagate ones are also most cheapest models.