No real preference. I haven't had any trouble, really, with either my Glock mags or my Springfield mags.
It's easier to spot the metal stainless mags on the range, but it's harder to keep my name or other identifiers on the mag body than on the plastic. The black plastic requires using a light-colored Sharpie or paint-pen to really show up well and are harder to spot, particularly in tall grass, but the markings last for a long time before I have to hit them again.
Both are easy to clean, and both have lasted me since I got into the sport/hobby nearly 4 years ago. I can't even count the number of cycles I've put through my four main training/range magazines for my XDm. I'd say that, conservatively, I've cycled each of those magazines 200 times, and the figure is actually more like 250. I don't practice with my Glock nearly as much as it isn't my primary carry/defensive gun, but even so, it's 5 range/training mags have got to have at least half that number by now, each. Defensive mags for each gun are stored for months-on-end, and I know from personal experience that even after storage of 2 years, they still feed just fine. They've been dropped on everything from concrete to rocks.
Blind choice SHTF? I wouldn't have a problem with either.
