I just bought my first AR, a S&W M&P15. I know very little about the AR platform. I would like to go buy 10 or 15 magazines for it. I will be taking this gun back and forth to "Ban" and free states. The gun itself is fine for NY. This rifle will be used for informal target shooting and woodchucks. What should I look for in "Preban" magazines? Do I want aluminum or steel? Is there any drawbacks to 30 rounders or 20 rounders other than the difference in capacity? Is there any design flaws I should avoid, or desirable features to look for? ( With steel AK mags I only buy ones with the back strap.) For free states What should I look for in new mags? Or should I just stick to older "preban" mags for my limited needs? I Know this Forum is not about brand names, just general guidelines. Thank you for any help.