I like MAG midcaps. (or at least the M4 mags, I haven't used the other) STAR G36 mags are complete crap, so I personally would stay away from STAR mags. (their armalite mags might be okay, IDK..)
You do have to break in the mag midcaps though. (by lubing them and then loading them and unloading them several times to disperse the lube and remove the excess)