What is the best AR-15 carbine with a quad rail to buy for a first gun?

Well, specifics depend on what exactly you want. If you just want a plinker to look "tacticool" with, you can buy a Del-Ton kit for $450 for everything minus the lower receiver. If you want an already assembled rifle, consider the CMMG "Bargain Bin" rifles, which go for $600, plus shipping and receiving costs.

Don't give in to the hype the mall ninja sorts on the AR-15 forum will serenade you with. They like to claim that anything which isn't Colt or Noveske is crap, they like to claim that any barrel which isn't 1 in 7 and chrome lined is crap, etc. It's a load of crap.

Unless you're buying an NFA full auto and firing off large volumes of ammo in one sitting, you're not going to benefit from chrome lining. In fact, it will actually impede your accuracy, due to imperfections in the chrome lining. Additionally, although many companies claim their chrome lined barrels to be "mil spec" (another claim to be taken with a grain of salt), they aren't actually lined to the military specifications. The end result is that the chrome lining eventually wears and flakes off, further impeding the accuracy of your rifle. And 1 in 9 is the rifling you want. It is actually the ideal twist of rifling for the 62 grain SS109/M855 NATO ball cartridge - the reason the military went with 1 in 7 is because it gives the same flight characteristics to the 62 grain ball round and the 64 grain tracer round. Hornandy actually recommends a 1 in 9 twist for their 75 grain .223 TAP ammunition. Unless you're going to shoot the 77 grain Mk 262 ammo, or the 80 grain .223 Wylde ammo (which requires a specific .223 Wylde chamber), then there's no need for a 1 in 8 or 1 in 7 rifling twist. I'd recommend a chrome moly barrel (chrome chamber, non chrome lined bore) with a 1 in 9 rifling twist.

As for quad rails, it all depends on what you want. You can get a permanently attached free float quad rail, or you can get a two piece unit which replaces the handguards. In both instances, I'm a big fan of the products made and marketed by Yankee Hill Machine. They make great stuff, and it's priced much more reasonably than, say, A.R.M.S., Daniels Defense, Bravo Company USA, etc. products.

If you need further clarification, recommendations on specific products, etc., you are more than welcome to email me at burningsaviour@wikianswers.com