all 3 lock specs are pretty even at the minute, with each spec being best for at least some of the fights this tier. i dontknow about pugs, on my server pugs are a thing of the past .
I'd say warlocks are overall in a good position right now. You'll have no difficulties getting spots for pugs, regardless of what spec you play. We've been dethroned, but being middle of the pack / semihigh isn't bad.
I am just sort of toying with the idea of coming back. I quit before MoP (Pandas turned me off, still do) but I'm kind of curious now as to how the world is different. I was always a demo lock before and I'll be honest all the post-5.0 changes seem very overwhelming to walk my way through now. The sheer amount of abilities even keeps me wondering if I can even keep track of that many keybinds. I'm just curious as to the play-style differences between the 3 specs now. When I left Demo was basically the steamroller with a complex rotation but high reward if done well (especially for burning through 5-mans), affliction was all timer and moderation of dots, and destro was big burst and lagged behind the other 2 in dps output. Is this essentially still the same just with different buttons now?