I dumped all of my metal Colt mags for Pmags. The Colt mags all seemed to have issues in a few AR's (One of them being a Colt). I love the metal HK mags, but can't afford to use just them so most of mine are Pmag anymore.
I like both but am partial to the the pmags. But neither one has ever failed me. Whether casually shooting or doing dumps. I think having a good mix of both is best. I have had issues getting the metal ones to seat properly before while the pmags went right in.
I like both. I am more partial to pmags just because of the grip but neither has ever let me down. I guess if you were gonna operating somewhere that was well below freezing you wouldn't want a pmag. Especially if it froze and got dropped. But I doubt any of us will ever be in a situation like that.