General consensus seems to be: 1-79 Solo – Spec whatever makes your jimmies tingle. 80 dungeons (or if dungeons are your preferred method of leveling) – craft yourself a build that offers quite a bit of utility in the way of applying conditions and healing your group mates. Currently I run Dagger/Pistol and Shortbow, with emphasis on blind spam and the 15 point Deadly Arts talent that makes you weaken when you poison. With this build I keep my target consistently blinded and weakened, bringing their damage to almost zero. I also make sure to run Shadow Refuge for stealth reviving and the ability to lay down a dark field (which leads to some awesome combos), and Smoke Bomb for the ability to lay down a smoke field (again, awesome combos).
For leveling, just pump deadly arts and trickery and spam 3 with double daggers. Caltrops too.