I hate CQB so I'd go with the sniper rifle - despite that I wouldnt label myself as a sniper whore. I just despise the run n' gun BS that this game revolves around. It's for casuals who are willing to trade. I can't think of another FPS - and especially not a competitive one - where running around like an idiot is a valid strat the way it is in this game. It's kind of like Gears but with more gimmicky abilties mixed up into it.
I enjoy fusion the most. I've gotten some flat out ridiculous kills with the vortex in trials and regular crucible. I really wish I would've recorded some of them.
Fusion rifle. But some of the maps are so small that you have to run with shotgun.
But most people aren't expecting the killing range that FRs have so you can get some pretty funny kills
My favorite was the would-be shoulder charger getting one to the face....