Depends on your playstyle, but its either QK or Gambler for solo. If you like to sneak a lot and you can avoid dangerous fights, go QK as you can get rid of mobs faster that way. But safer way is Gambler, especially when HD comes live. If you are gambler and accidentelly pull some larger group of mobs or some tough mob, theres better chance you come out of that fight alive.
Originally Posted by Markovnikov
Before HD, true gambler benefits were noticable at lvl about 55+ (with legendaries with gamble legaces, with blue capstone and with more blue traits), but when HD comes live, its probably good to trait gambler even sooner because Bob and Weave is very nice to have for soloing i would guess.
Naius - Burglar of Withywindle