As @Nery said: Purifier is currently the “go to” class for anything with ranged weapons.
Here’s a current gunslinger build:
Given the inherent strenght of Purifiers, basically any somewhat decent fire setup will work…
Other less common options are Paladin and Pyromancer (a classic).
Paladins are about S&B, holy light and stuff. Right? RIGHT? 
If you want a glass cannon with incredible dps, there’s still the classic Darkblaze Pyromancer:
Be warned: The spec only works if you have the required gear - especially Darkblaze set is crucial.