Beam Lasers. Reliable as a weapon can ever be. No lags, no hit detection problems (for the first several hours of game, at least). And easy to control.
SRMS. SSRMS, when the bug will be fixed. Great damage for ton, cockpit-shake. Remember reaping 2 Bushwackers in close with SSRMS on Vulture B.
UACs are just powerful, but not my favourite.