i should mention its for PVE. And i heard Vanguard (also Powertech) is bad on DPS. IS that true?
Vanguard/Powertech DPS is actually rather good. Assault Specialist/Pyro is the #2 overall best single target DPS in the game after Watchmen/Annihilation Sent/Maras after both received buff in 2.8. Both regularly parse over 4000 in the best gear, and as everyone has said, AS/Pyro for Vanguards and PTs is about the simplest spec to play. Tactic/Adv Prototype is also very easy to play for VG/PT. Vigilance/Vengeance Guardian/Jugg is fairly simple (5-6 ability rotation, very predictable). Telekientic/Lightning Sage/Sorc is a very easy rotation as well in my experience.