For Destruction you'll want to sacrifice your pet. If you're facing a lot of casters/healers, go with the felhunter. Otherwise, just go with what you feel like. The voidwalker health boost can be pretty epic.
As for talents, I normally go Dark Regen/Shadowfury/Dark Bargain/Blood Horror (but this can be substituted with Unbound Will if you have a pocket healer)/Grimoire of Sac/Kil'jaeden's Cunning. An argument could be made for Archimonde's Darkness in certain cases, but you'll be moving a lot in random BGs.
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One would think that someone who plays a warlock would know their strengths as well as their weaknesses. And more importantly, what the hell one of our most powerful talents do, and what the downside to using it is. I've had three different warlocks frag themselves on my pimped-out UA via Unbound Will today, and one of them even did it twice.
I'm having a hard time figuring out what spec to use in BG's/RBGS. I feel like destruction doesn't really do a lot of damage, and since most of your abilities are casts, I find 99% of them are either absorbed, reflected, etc, something, it's just extremely irritating doing literally awful damage.