I've stopped using Blacks - maybe I've just been unlucky but in the 119 drives I bought last year for work+play, only 3 were WD Blacks - all three failed and they are the only ones out of the 119 that have failed. I wouldn't mind so much, but the blacks were all for me in different machines, so I was the most affected. I'm more than happy with WD in general, using Reds and Greens extensively, but I look for alternatives to the Black series now. Maybe I just had awful luck /shrug.
Personally after that experience, I'd have 2x2TB green (or red - both cheaper than black) in raid1 - with most raid codecs, you'll get a read speed boost (higher than a single Black), a slight write speed hit and some data protection with two drives having the same data.