Thats funny, I almost exclusively use shotguns. I find the assault rifles to weak. I really liked the sniper rifle but it's just too weak for when things get in close.
I've started using the quasar as a support weapon so that forces me to rely heavily on my primary as I have to wait so long for it to fire and "reload".
What do you usually fight with the shotguns? I really want to like the shotguns, but every time it leads to more deaths. The only support gun that seems to kill things easily for me is the Scythe.
Personally I like the Punisher's stagger effect, especially on berserkers. I've heard people use it to stop hunters and spewers too. But I've never played on higher difficulty levels.