Stick to a company that has a good reputation. Colt, Bushmaster, Rockriver to name a few. The larger companies have repair policies that should reassure you. With that said, I co-worker had a Colt Match Target that would not shoot better than 3" groups. Sent it back and they said the accuracy was with in specifications. 3" groups acceptable? My Colts, one carbine and one rifle will shoot 3/4 " groups all day long.
I hear bad things from Armalite, but anyone can build a bad rifle.
Bad thing about Ar's is they can be had for a low price, which is highly subjective to the person buying it, but generally they aren't regarded as quality Ar's. You can build one from a Kit for $650 or so and end up with a pretty good Ar but from a reputable company you are looking at $750 or more.
I have had very good luck with Bushmaster and Rock River Arms. Have see some very good rifles that are built with Stag recievers. Another one to check out is Smith and Wesson M&P rifles, very solid rifles. I know when they first started out I believe Stag made the recievers for them. One NOT to get is the Olympic Arms Plinker, or any other with a cast receiver. AR rifles that are in the service grade should have chrome barrels, It increases barrel life and cleaning is much easier.
You can buy any model Bushmaster from Davidsons, on line thru the local dealer of your choice. www.galleryofguns.com Any gun you buy from them comes with a Lifetime Free Replacement Warranty. I have already used their warranty on a .22 Ruger handgun I purchased thru them. I took it to the range and after about 80 rounds, it broke, (trigger wouldn't reset). I took it back to my local dealer and had a new one in my hands the very next day. You simply can't beat it. Bill T.
If you are willing to try something new, learn alot in the process, and save a few $$$'s, you can put one together yourself, either from a parts kit or buying a complete upper and complete lower. Check out Del-ton, J & T, PK Firearms, to name a few, for complete uppers and complete lowers. If you shop around, you could get into a complete firearm for under $700 easily, maybe even under $600.
The other way of course is to find a complete rifle or carbine, preassembled. This way, you also get the security of a warranty, even though most reputable brands will also provide warranties on parts, such as the complete uppers and lowers.
As for brands, that's like shopping for a vehicle. Everyone has a favorite, based on whatever. You can't go wrong with the major brands, Colt, Armalite, Bushmaster, Rock River Arms, DPMS, Stag, to name a few. Or if your wallet is bottomless, check out Les Baer, Wilson Combat, JP, etc.
Find your comfort zone $$$-wise, then check out the internet sites, like this one, to get ideas, and do some searching. Good luck on whatever you find.