Of course, personal play style will play a big role in the matter, but if you want the statistically correct answer, the best build is:
Incendiary grenade
Better Control
Deadeye
Incendiary Blade
Gunslinger's Trance
Chain of Woe
As far as the stat boosting perks go, Path Unknown + Way of the Fearless is easily the most popular, but the success rate varies by playlist much more than the other talents I listed, which are all consistently the best in their columns.
You can look for yourself at
http://guardian.gg/en/subclass/gunslinger