Well all of the classes play a role in end-game(pvp)
In my opinion, if you really want PVP or End-game I'd be a rogue.
Reason why: Rogues have stealth and have the ability to gouge or blind someone. In that state, they can easily crit them if they have the appropriate equipment and skills. Also in end-game, you'll most likely be the one with the highest threat.
Build: For a dagger build use this:
http://www.worldofwarcraft.com/info/cla ... 0000000000
Explaination: Most experienced rogues agree this is the #1 raid dps build. White damage boosted by Slice and Dice provides exceptional sustained damage. If you want to be #1 on the damage meter, this is the build for you. And as a bonus, the changes in the Subtlety and Combat trees also make it possible to take some pvp-specific talents.
The key talents in this build are Imp SnD, Imp Backstab, Opportunity, Dual Wield, Blade Flurry, Weapon Expertise, and Adrenaline Rush. Malice, Relentless Strikes, and Dagger Spec are also important.
And for a sword build use this:
http://www.worldofwarcraft.com/info/cla ... 0000000000
Explaination: Another old stand-by, this is the highest dps raid build for swords. It won't match Combat Daggers for sustained damage, but it's a bit more adaptable for various types of fights. It's also the best build for lvl'ing up and solo grinding.
Key talents: Imp SnD, Imp SS, Precision, Dual Wield, Blade Flurry, Weapon Expertise, Adrenaline Rush. Once again, Malice and Relentless Strikes are also important.
Variants: The four points in Lethality and Imp Poisons are definitely not needed unless you want to squeeze the last drop of dps out of this build. You can easily move those points into the pvp talents in the combat tree or even MOD in Subtlety.
PVP Strategy: For the dagger build, you would most likely use stealth, slice and dice, gouge, and backstab. I've seen many rogues that use this build PWN ME. Almost all the rogues that I have faced with this talent build usually kill me in 2 hits. My main is a hunter, but I do have a twinked lvl 49 rogue.
For the sword build, I have not seen anyone use this type of build because most rogues prefer daggers than swords.
I hope this helps you make your decision.