I shot a run runner guns upper and an anderson lower gun and my 1968 20rd colt mag feed steel case all day long, the upper had issues with the pmag, don't really know, but those old colt mags run and run and run.
I use both mags. I have had pmags split on me.
All things considered I'd say they're fairly equal. Each has it's pro's and con's, but for the average shooter they'd more than likely rarely be let down by either. When out in the sticks training though, I do tend to lean more towards surplus AR and AK mag's for the simple fact they don't crack if you go down hard on them; They might dent or crush, but 99.9% of the time you can do a field repair and continue using it.
I have both, in 20 and 30 round models. They all run perfectly.
Edit: I was at the range today with some rounds loaded into stripper clips. The aluminum mags loaded perfectly, but the Pmags had some issues. the groove where the charger spoon allowed some slack, so the rounds hung up going into the mag. Initally it worked fine, but the plastic on the pmags wore out quickly with a couple of loads, and then every thing jammed going in. I had to hand load the pmag.
