Firerate...because once you reach a certain point, individual damage and accuracy don´t matter anymore. You just pump out a stream of lead more destrcutive then a laser...and looking like one when spiked with tracers!
"Oh what´s that? Your rifle has a basedamage stat of 300? I only have 20...what? You can only fire 10 RPM? DUDE, I can go 3500 RPM and have a 5000 round container in my Blackhawk, so fuck you."
When not in a Blackhawk or having a rotary cannon handy, LMGs tend to do the trick.
Also, I´m the close range encounter guy, and an SMG going 900-1200 RPM with a big magazine is still going to be a shitton more usefull in ranged engagements then a shotgun, which are always underpowered in most Videogames.
Also, more Dakka. Because you can never have enough.
There is also a reason why guns on Aircraft tend to be rotary cannons, because with that kind of lead going down range, something IS bound to hit. And if you saw the GAU-8 in action once, you don´t argue about damage anymore XD
To me, a crucial stat is "Damage per Second", how much damage can I get out in how much time. What is individual shot damage gonna do if you have to nail EVERY shot in order to kill slightly faster then some dude spraying you with 30 rounds in the same time, of which only 3-4 need to hit to kill you.