Rogues have lots of viable pvp specs in vanilla.
Prep with hemo
-great survivability, 2x cooldowns, cheap combo points, best for stunlocking
Prep with imp backstab
-same as above mostly, possibly better burst using backstab instead of hemo.
Note that you can still use ambush with a hemo build if you want, you just use a weapon swap macro to switch between mainhand sword/dagger. So it pretty much comes down to if you prefer hemo or backstab.
Seal Fate
-like Prep with imp backstab, but trades survivability and control for even faster burst, works best against clothies
Combat swords or maces
-best for raiding/pve, but can be great in pvp too, adrenaline rush is straightup overpowered in the right hands plus other good stuff like riposte and bladefurry
Here's a pvp video by Grim.
http://www.warcraftmovies.com/movieview.php?id=243248 He uses Seal Fate, Combat swords, and Prep with hemo and wrecks with all three.