The only mag-related malfunctions I've ever gotten were double feeds from two different pmags. Keep in mind I've used them a lot more than metal mags.
I think I'm leaning metal mags these days. They're a good bit cheaper, fit in mag pouches easier, fall out of my rifles easier and seem just as reliable to me. I really dig the Lancers, too.
Point is you're probably fine with whatever mag you get, provided it's from a decent manufacturer. I've had zero issues with C Products, NHMTG, D&H, Lancer and Fusil.
The Fusil mags are super cool. I picked a couple up for like $12 ea. one time and they are my favorite mags of all time. Not worth the $39 retail, though.