M590 is best...
I LUB SHOTTIES CUZ IMA SHOTTY NUB.
I ended up being first on my team using a M590.
The high rank people screamed shotty nub and i actually got an ultra kill with the M590 pretty fast. 2 HIT KILL FTW!!!
Double Barrel! I've gotten 5 kills with 1 right click.
I approve of this message ^^
However, it is almost impossible to use this in a 16 OMA.
I've used both the Super 90, and personally, the M3 is a R870 on steriods or at least a R870 MCS without a scope since it retains the spread and rounds per magazine but with more portability. I can't really feel the recoil of a shotgun so it doesn't bother me. Price wise, it isn't worth it if the M590 Military is cheaper.
The M4 is another story... if you can control the automatic fire of a shotgun, then this comes very close to the M590 Mariner CQB but with a much faster fire rate (kind of like a Spas-12). I think it also has the same spread as the M3, so that makes you more of a shotgun noob.