In the past year I've had these failures: 2x WD RED 4TB (EFRX), 2x WD RED 6TB (EFRX), 1x Seagate 4TB. I have a fairly even mix that includes HGST (and a few HGST He). No HGST failures yet. I won't be buying WD RED's for a while, if ever.
To counter that, I've been running 11x 4TB WD Red (WD40EFRX) since 2013 and zero failures, with 10 drives in RAIDZ2 and 1 warm spare.
I have them in a 4U chassis in the attic, with 5 case fans blowing through; two on the rear and three across all the bays. It's a 24 bay box, but I've not yet had pressing need to fill the rest of the bays.
