Re: AR-15 Mags
I have always been a little skeptical of the plastic magazines especially after having some Thermolds become thremelts. Pmags on the other hand are not only reliable but inexpensive and can be had in fashion colors. I did my own evaluation and after taking several out to the range and abusing them and using them on a daily basis for years now I am sold on Magpul's Pmags. I threw them against walls, (filled and empty), threw them across the range on concrete, repeatedly let them drop free with them full and empty, ran them through suppressed sustained rates of fire (5-6 mags in a row as fast I could get rounds down range and make mag changes) with no melting or charring of the magazine. I even ran over a couple with my truck just for shits and grins and they still worked. The only real down side I have found with Pmags in they are a tight fit in standard magazine pouches made for the aluminum GI mags.
Keeping the dust cover on the filled magazines is important and does help save the feed lips from becoming distorted. The slightly larger design and texture of the Pmag helps in getting a good grip on the mag in wet weather or with gloves on. Aluminum mags work like a champ and are reliable but usually only after my old surplus ones have been upgraded with new anti-tilt followers and new springs (bringing the cost to that of a Pmag if not more). Another advantage to aluminum is if your feed lips become bent or distorted they can often be reshaped and put back in service unlike broken lips on a Pmag rendering it questionalble at best.
Bottom line is how you want to spend your money and hopefully realizing that rifle magazines are a consumable piece of kit and changing them out is the cost of doing business.
A couple things to remember/consider with magazines are to inspect and clean them regularly. Magazines are often the source of malfunctions so if they are not reliable mark them and only use them for training malfunctions and failure drills. A trick I have found with the Pmags is to take a string or single strand from some gutted 550 cord and tie it to the hole on the rear of the dust cover then run the other end through the drain hole in my mag pouch. Have enough string length to allow the dust cover to clear the top of the mag pouch so that it can be reattached when the magazine is filled and stowed in the pouch with rounds going down. When you pull your magazine from the pouch the string retains the dust cover for you. This does generate a little more tension on the magazine but is easily overcome with training. Always keeping covers on has helped to maintain the feed lips shape, keep trash out of my magazines, and helped to keep from losing my dust covers.
Good luck in your quest and let us know what you go with.