I've had a Purple drive fail soon after use, about a month into it's purchase. I'd say to keep clear of the Purple drives, unless that is the only drive you have access to. IMHO, I've had multiple failures for drives made by WD though I've seen failures from other brands as well. Best practice is to backup all critical content and not have it on a drive when it's dead.
i was looking at forums and saw seagate drives fails often too, i read that WD blue's are durable brand for hdd's i dont know what drive to use for my storage though, i got tons of files and my case can only support 2 3.5" hdd's.
If you don't need a performance drive the large blue or greens run cool due to their 5400rpm speed.
If you need performance I would suggest a WB Black, they have a 5yr warranty but cost more. I have several green drives, Seagates, Toshiba's, and have used many blue drives and the only issues I've had are with 2 of the 9 Toshiba's.