The 10 mm Smg is awesome. Plentiful ammo, fast fire rate and a good dps. I use mainly for a hallway clearer. A lot of people prefer the combat shotty for that, but I understand the power of having that extra range. I'll keep the shotty for small rooms and ghouls.
I agree with you Cory about the SMG. I love them. The vanilla one is great. Although my favorite use for the SMG is ghouls (ghouls; not Reavers), unless I'm using something like a lead pipe.
And, Sydney's SMG is good throughout the game as it's DMG is very high.
I like to pair LR with the SMG. LR + Sydney's SMG is especially great. ( with added bonus if I had to do something terrible to Sydney to get it
)