No go for SB, they r easier to lvl than hunters and they r very strong if you spec the right way. Always go for max Poison. Thats the key. When ur in Thidranki (BG for 20-24th lvl) u can have a skills boost of +5 max. So put 20 pts in Envenom and with the +5 ur going tu use the 25th level poison, the most powerfull u can get for that BG. Second, Cap ur Weapon or/and Critical strike, so go at least 21, so +5 ur caped. A good thing about SB is that its the only stealthers that can use 2-handed weapons... I made two SBs for Thid and my specs were that : 21+5 Sword, 20+5 Envenom, 19+5 Stealth, and for the other one i put 21+5 Critical Strike instead of sword. Both were fun to play, but 2 ways of playing... The one Sword-specced was easier to play, could attack from every angle, even soloed a Blademaster without taking him by surprise ! The other was harder to play, but fun too. U have to be always looking for positional, to get ur PA or BS, and when u do u rape them. But when u dont, ur dead :)
I hope it helps :)