I'll have to say Fusion Rifles. They're the only gun you have to use with timing. With a sniper, you can bodyshot if gone to crap. With a shotgun, you can pull the trigger again or melee. With a sidearm.... Spam more bullets? But with a Fusion rifle you're dead. Charge time needs to be taken within your knowledge on the enemy movement and time it so. Otherwise you shoot badly and note that your head is filled with bullets.