I've am a pretty heavy pvp'er and love the bg's, and aff is a good spec if u just wanna spam dots until you become enemy number 1. But i have to say the crits of destro works better for pvp, it kills things fast (realz fast) and bc ur a 70 u have enough points if you use them right to still get allot of the benefits of the aff tree. I would highly recommend these two pecs.
This build allows for all the crits of the destro spec and all the dot damage from corruption and the benifits from soul siphon and night fall. My other pvp spec would be
this. It main DD is shadow bolt but it's nice reach into aff allows for good dots.