Sorry that I missed this earlier. I wasn't online much yesterday.
I have the CAA, the AFG1, and the AFG2.
The only difference between the magpul versions are the wings that the gen 1 have. The gen 1 seems to be better with handguards that are more rounded. The gen 2 is better for wide and/or more squared surfaces.
The CAA/MAKO/FAB is also very comfortable, but I think for a shotgun, the magpul works slightly better because the forward "hand stop" gives your hand an anchor point when you're pushing the slide back forward chambering the next shell.