Guild Wars 2

thief or mesmer or d/d ele is betetr for that ?

Mesmer is one of the best classes for spvp/tspvp. Thief can be very good, if you know how to play. Ele can be good.

d/d ele.. its definitely the easiest. Pretty much a faceroll class, and if you are good with positioning and rotation then you can carry your team to victory easily.

D/D Ele with celestial is the easiest to play out of the three, and it can deal good damage and off tank. Thief and Mesmers both have to roam and support the team with far caps and quick kills, mainly by being bursty. Both of them are harder to play and if you are bad to average with either you will be a liability. Thief is slightly easier to play than Mesmer in an S/D set-up. With both classes never build for stealth in PvP.