I generally like milspec with magpul followers--but not old worn out surplus ones. Lots of folks like the magpul mags in general.
And for the "newest thing" in AR mags you might investigate the "Easy mag"--I've no hands on experience, but they have an awesome marketing video where they fill 'em with sand, shoot 'em with shotguns, run 'em over, etc and they still go like mad. But, they may just be gimicky--I'd like to hear some actual users on those before I sank money into them.
Some ARs are finicky as well--my oly has a very tight magwell, not everything fits up in there.