I'm running 4x 80 locks in pvp right now, and my findings so far are affliction all the way.

On paper destro burstx4 sounds sexy... but its exactly like trying to play elemental shaman, except naked and with no totem protection. It just doesnt work very well.

I made a lock team for a breath of fresh air compared to my shamans. Affliction is so EZ mode to play and its super effective. I played Demo as well... and it's really lackluster even x4. Ya felguards are fun, but they won't solo any real geared enemies. Metamorphosis needs so much work to make it worthwhile. I liked it but truly it was only fun for guarding AV towers (4x immolation auras + hellfires = lol aoe dmg)