in my diverse enterprise enviroment
there are 2 types of WD red drives, one is 7200rpm ( pro) the other is 5400.
I use WD black drives now (uber premium) for most of my NAS units they come with a 5 year warranty
I used to use WD red pro except they have a high failure rate for the 3TB models and i am bound on some of my NAS units to 3TB drives.
I have used the enterprise models, tan and the black and yellow ones they are good now worth the extra money though.
I have seen the WD green ones in some NVR's and they fail after about 3 years on average.
seagates get thrown in the garbage if i see them
Hitachi would be my second choice but they are pricey
in regards to the drive speed i have found that a 64MB cache and 7200RPM is a perfect medium when you factor cost, performance, and ROI.
SAS drives are a waste of money as are SSD's.