PT/Vang, Mara/Sent, Sniper/Gunslinger if you want DPS
Assassin/Shadow and Scondrel/Op are also nice. You will lose some DPS in trade for utility (stealth, etc) As a sentinel the class I hate the most is an Op. When I mark the ones that buttpoke I typically stay away from them cause you can expect a hard long stun and a major *** rapage.