Orc should be.
Trolls racial kinda loses value, as haste capping is ( However, it also depends how the rework the RoF (For single target).
---------- Post added 2013-06-17 at 09:35 AM ----------
Goblins is kinda "middle tier", Orcs/Trolls is better for Aff/Demo anyway.
Anything but belf, if you go pvp go undead, or well min max undead is best since it's the most emo race. The more emo irl and ingame the better you get at warlock.
as far as optimal DPS goes, unless you're in a proper progression raiding guild, i would say it doesn't make a huge difference.
if you wanted to do a fair bit of PvP i would say definitely orc or (as i am) undead, for pure PvE i'd say orc or troll (or potentially goblin, idk). best looking IMO is undead or orc anyway. my lock started undead, then i faction changed to join a progression guild and was human, then dwarf when it became available, because dwarves. now i'm back to horde, had belf for about a month, hated it, and went back to undead. i love the fear trinket too much and the casting animation is just badass.
so yeah, unless you absolutely love the look (and casting) of belf, you're better off with pretty much any other race