Hammerburst. I haven't played since I finished my achievements so I don't know about the new updates but back a few months ago I would destroy teams with my hammerburst. I got called out for using a modded sooo many times, even my friends couldnt be convinced. Honestly its not about how fast you shoot, its the rhythm, there ARE cooldown times between shots. You just have to find your groove and you can just eat people alive with the thing. It's the number one weapon besides your one hit killers (boomshot, torque, sniper). Personally it's my second favorite weapon, which is nice, since you are always holding a power weapon

2.0 kdr talkin here so you decide whos right
Also I use hammerburst in campaign as ammo is everywhere so you can let loose.
Also I need to add that you should always ditch the shotgun, because hammer>shotgun easy. I absolutely love shooting a two-piece scrub without walking backwards when they are point blank because they mistime their melee because they didn't calculate the stopping power of hammerburst and melee too early. Shit is so cash.
I could talk all day about this weapon, I basically used to advertise it and bash lancer users as automatic BKs unless they were using it for fun. Still do.