I went for critical skill tree and some points in sniper for fast reload and heat management thingy. Works great and is fast. The best heavy weapons currently in my opinion is heavy boltgun and plasma canon.

The combo I went for though is boltgun(the nonheavy version) for clear/run speed and plasma for big guys(right click channeling skill is good deeps). For armor till the newest patch I used assault for additional group clear. Now it's a bit longer cooldown, but it seems to be better at tracking enemies. Now I play sin mainly so I didn't test sentinel armor. Turret was semi good distraction for enemies and small bit of dps, but wasn't worth it. Maybe it changed with current patch?

For granades I used good ol frages for again additonal group clear. Stun and flash seems kinda meh.

Bare in mind there's no bad weapon in the game(well maybe a one or two like flamers). They are just usually slower at killing or can't kill through regen, but are great at clearing normal enemies(grav gun). I really hope neocore won't nerf the bolters and just buff other guns.