I'm not big into M4s, ARs or "battle rifles" at this time.
Time, training resources and $$$ being the main issues.
If I were looking for some serious, well made AR magazines I'd snag a few HK 416(fits in ARs/M-16s), the popular Magpul or the cool, high tech model I saw that goes from green to yellow to red so you can keep track of your rifle rounds at a quick glance.
Im not sure of the exact brand name or price but it may be here:
www.Brownells.com www.Cheaperthandirt.com www.NatchezSS.com .
Brownells is a great shooting sports/gear company and puts out a entire printed catalog of AR parts, magazines and related accessories.
All the best:
Clyde F