When the AR 15 first came to the market, the options for magazines were aluminum GI mags with regular followers or green anti-tilt followers. Things have changed quite a bit since then with a ton of manufacturers and options on the market. Like anything in manufacturing, there are good and bad options. While it's good to know what not to get, it's better to know which you need. These are the top 3 I've found currently on the market; I've personally had experience with 2 of the three options I'm going to list here.
Magpul is the top name when it comes to magazines. They are used by everyone from recreational shooters to hardcore military and law enforcement personnel, for a good reason. They are the perfecters of the polymer mag combining the right mix of flex and durability. One of the main problems with GI mags are the feed lips. When they get wore out, struck or stepped on, they bend. Trying to get them back into that perfect shape is impossible, once bent out of shape. This causes problems with feeding and proper cycling while firing. The nice thing about polymer is that it may bend but, due to the composition, it flexes back into shape. This means they can take a ton of punishment without failing. It doesn't end there either. Some of the benefits include a self-lubricating anti-tilt follower, USGI-spec stainless steel spring (for corrosion resistance), constant curve geometry for consistent feeding, and textured surface with a flared floorplate for better dexterity during mag manipulation. Magpul has a plethora of options to choose from that range in color, capacity, and caliber. Prices range from $12.95 to $129.95. Available just about everywhere and even in package deals with optics and ammo, definitely the go-to for any shooter, myself included. If you haven't yet, get some and you'll see why. If you have, get yourself more because you can't have enough magazines.
Troy Industries is well known, in certain circles, for AR 15 accessories. I had an opportunity to put my hands on these a few years ago, and I was impressed. I have several friends that swear by them too. Made from military-grade, chemical, biological, and impact resistant polymer, they are built to last. They come with reinforced feed lips and an anti-tilt follower, which allows it to be stored, loaded, without fear of the feed lips spreading over time. They are textured on the outside with a scale pattern for a solid grip, no matter the situation. Finished with a bolstered, flushed floorplate for easy manipulation and what’s nice is they stack evenly in your safe with other mags, making them more convenient for storage. They also come with an extended shock absorbing floorplate (a $5 value) to give you an option on how you pull the mag in the field. You can find them online for anywhere from $10.99 to $13.99 and even as a three pack on the Troy Industries website for $35. They are a solidly built polymer mag that has the shooter in mind and a reasonable price to match.
Out of the mags I'm listing, this is the one I've never tried. If you want a standard GI style aluminum mag, but with some upgrades, I'd recommend giving these a try. The reason I chose this company is that they are everywhere, and all the websites I searched had excellent reviews. After reading on ASC's website about their features, I can see why. Made of 6061 aluminum, heat treated to T6 condition and hard coat anodized to mil-spec standards, they are rugged. They also contain chrome silicon springs and a mil-spec polymer follower. A big bonus to these is their proprietary, durable exterior coating. Not only is it available in several different colors, but the coating is a wear-in, not a wear-off style of colorizing. Meaning the mag will stay nice looking for years of use. The coating also has a self-lubricating property that allows for smooth function and little upkeep. The standard 30 round mag and colors are $14.99 with a pink version for $17.49 (a portion of the sale of a pink mag is donated to breast cancer research). If you want that GI look and feel but with a bit more reliability, check out ASC aluminum mags. The number of recommendations and good reviews says they are worth the chance.
Magazines are an inexpensive way to upgrade or personalize your rifle. Any shooter can tell you that they don't last forever and you can never have too many. While there are cheaper ones that I listed, you get what you pay for. These manufacturers are reliable, functional, and recommended for a reason. The main reason for replacing or changing mags is feed and function issues. An issue that can cost you time on the range or possibly your life in the field. So, make sure you have plenty of mags and that they run well.