Dusting guardians with a fusion. When I need to. Zapping and melting a guardian with a fusion is quite entertaining.
Recently HC/shotguns have been fun as well.
Its subjective with the map/mode/encounter/range.
1v1 a fusion will probably win.
1v2(or more) a shotgun is very useful.
Camping in a corner of a map, Sniper rifle.
Should have had a All of the Above vote.