What Features Should I Look For in an AR and Which I Should Avoid?

BUY NOW! GREAT DEAL ON A NEW (Insert brand name here) AR!

Yeah, I get the emails too. I occasionally read the forums. I'm told I have to follow the ABCs (Always Buy Colt) because It's "true" Milspec and nothing is better than Milspec. Or, I have to spend $2500 because Noveske makes the best ARs and every wannabe "operator" absolutely cannot hit a target unless they have one of those rifles. Both of those statements are fairy tales. But, we are interested in buying ARs and we have to choose, so what features should we look for when making this important buying decision? 

To me, you first have to define the POU that you're buying it for. If you are buying a CQB rifle, for home defense, that makes a difference in the features you want compared to a competition 3-gun shooter. So, understanding how you want to use it is key to knowing what features you want. Once you've established what POU it is meant for, then you can move on to looking at the specific components and materials.

Quality Materials: 

The first thing I look at, after POU, is the materials. 

1. For the body (receivers) of the AR and the buffer tube, I'm looking for 7075 Aluminum with T6 heat treat. If I see that those parts are made of 6061 or some polymer, I stay away. (At least for ARs. It's fine for hanguns, but not a fighting rifle due the differences in energy and jam-clearing procedures.) 
2. As far as barrels, I want a good steel, typically a Milspec Chrome, Molybdenum, and Vanadium (aka CMV, chrome-moly-van, or chrome mov) mix, with a chrome lining. Getting a barrel Cold Hammer Forged will add life to it, but it comes at a premium price. Any chrome-lined barrel from a reputable manufacturer should last well over 8,000 rounds before throat erosion becomes a problem - they are just fine. I would stay away from most stainless barrels because they simply wear out too fast.
   
3. The best commonly available steel for a bolt is still 158 carpenter's steel. 9310 is also very good and you'll be fine if you're running that. S7 is excellent steel, but the only company I'm aware of that is producing s7 bolts has had issues with their heat treat process. If you're willing to try their bolt, S7 is superior. 
4. Most other parts are more about ergos and weight than ultra-durability. Buy from a reputable company and you'll be fine.

Components: 

There are certain types of components I prefer and some I do not want. 

1. For starters, I want a collapsible stock so that I can comfortably use the gun from different positions, with or without a plate carrier, and so that I can have a family member with different arm lengths use the gun. The collapsible stocks are typically lighter than fixed stocks, which is a significant advantage.
2. I use M4 flat top receivers for mounting optics. This is a huge benefit of the AR platform, so going backward to the carry handle/sights of the 1980s is not the best choice, in my opinion. This is almost standard now, but make sure they have M4 feedramps as well.
3. Barrels are the most important part of your rifle, so I'm going to cover them more than anything else. When selecting a Barrel, you need to get a set up that works and is legal. In order to avoid NFA costs or pitfalls, I go with 16" or longer barrels - they also add velocity to the round with the extra length, so that is a good thing. I also find that mid-length gas systems (paired with H1 buffers) on 16"-18" barrels are ideal, but the typical Colt Carbine gas system is reliable as well - it's just a little over-gassed. Again, ensure it has the M4 feedramps. I prefer barrels that are the same thickness on both sides of the gas block seat, but I look for a barrel that weighs 30 ounces or less, preferably 24-28 ounces. I want it thicker and more durable than a "pencil" barrel. Also, understand that the weight of your barrel is going to be at the front end of the rifle, so it'll slow your movement with the rifle. Any reduction in weight of barrel is going to improve your mobility. Along those lines, I avoid government profile or m4 profile barrels because they are front-heavy and the extra weight is totally wasted because the weight is in the wrong part of barrel, at the end, so it doesn't help accuracy - it just increases weight. Under the handguard govt/m4 barrels are basically pencil barrels, but they're heavy at the end, so they're some of the worst profiles for fast movement and accuracy. In fact they're the OPPOSITE of what you want in a barrel for accuracy and movement. (I'm sorry to our troops. If I could speak to your commanders, I would.) I also would avoid "Bull" barrel profiles unless you are just making a bench-rest shooter that is meant to be highly accurized. The ideal is a barrel that is heavy enough to be sturdy, avoid significant POI shift from heat, and somewhere under 30 oz.
4. I also find a2 front sight posts annoying. They impede vision through optics. I prefer flip-up sights or 45 degree offset sights.
   
5. Since I have no A2-style front sight post, I can use free-float handguards. The free float handguards provide better accuracy and more real estate to attach a light and vertical grip, as well as more area to put your hands.
6. I also look for single stage triggers in a fighting rifle - reliable and simple. These two stage triggers are good for competition shooting, but I'm not going to be taking advantage of the benefits of a two stage trigger when I'm fighting for my life. I just want it to work every time, so I prefer mil spec style, single stage triggers.

Accessories:
Got to accessorize, right? Well, there many useful things to add to you rifle. 

1. Optics are a huge part of that. Red dots or scopes make a HUGE difference in your effectiveness with your rifle. Which one you need is governed by POU. What I really want is one with a useful reticle or dot display - and it better reliably hold zero. 
2. Lights are essential. Why? So you can identify your target and see what is beyond your target.
3. Ergonomics are huge as well. Can you grab the handguard comfortably or is it a cheese-grater? Is the handguard too fat? Is it too slick? Does the pistol grip fit your hand well? I find that I prefer BCM Mod 3 or Magpul K2 grips, but we're all different, so feel the grip in the position you'll be holding the gun.
4. Keymod, M-LOK, or Picatinny attachment types each will do the job, but I would steer clear of the "quad-rails" with 4 Picatinny rails at noon, 3, 6, and 9 for weight-reduction purposes.
5. You may want a Vertical Grip or a bipod mount. If you do, Keymod and M-LOK are great, but you'll have to search for a bipod adapter that you like and that connects directly, unless you want to add a Picatinny rail section and then add the bipod. I look for things that connect directly with Keymod, so I don't have to add the extra weight.

Hopefully, this gives you some ideas on what to look for when you're buying an AR.  Especially for people who are new to the platform, or just new to guns, there are so many options for the AR that it can be dizzying. I recommend you check my article "Builder's Component List"- you should be able to see many of my recommendations and see what kinds of things I prefer, which will hopefully give you some ideas for your rifle.