I'm not an AR expert by any means but alot if depends on what you are doing with the rifle, and wether or not it will have optics or steel sights. A couple of things that are a must as far as I'm concerned is a good quality trigger, and a good sling. If you are going with optics a bipod and a tactical charging handle are needed to help with ease of use.
I'm looking at both routes. 10.5" to 16" carbine build w/ iron or RDS, or a longer 20" rifle build w/ optics. More or less trying to spur on some discussion about individual components that have been found by members to be worthwhile.
LMT 10.5 upper
Troy flip front and rear
Noveske KX3 flash suppressor
EO Tech 512
Magpul Miad grip
Magpul CTR stock
This is what I am working on for my next build.
Here are the mods I did on my DPMS LR 308 and I love it!!!!
Super Sniper Scope,
Badger Ordnance Rings,
a MagPul PRS stock,
a lewis machine and tool two stage match trigger,
a badger ordnance tactical charging handle,
a MagPul MIAD grip,
and a Harris Bipod.
If you're going to scope the AR, a 20" barrel is suggested. Get a scope mount that moves the scope a bit forward if you plan to shoot prone since you'll find a massive lack of eye relief otherwise.
Two-stage and match triggers are nice, but they seem to have problems with longevity, especially under rough use. The basic single-stage that came with my DPMS lower parts kit has about 4mm of travel and a clean break, so I question the value of fancy triggers. YMMV.
If you get a collapsible stock, make sure you get one with a mil-spec buffer tube since it's more difficult to find decent collapsible stocks for the slightly larger "commercial" buffer tubes.
The Aimpoint knockoffs work about as well as the real thing, but noone is sure how well they will withstand rough treatment...
You can spend a fortune ricing out an AR if you so desire. Whether you will benefit from having an AR loaded with accessories worth eight times as much as the AR hiding underneath is questionable.
Larue seems to be seeing some serious competition from American Defense in terms of quality optics mounts.
Rail systems are pretty nice for mounting accessories, but can get stupidly expensive. If you're doing a 16" AR with a dot/reflex sight, a monolithic or freefloat rail system seems to do little save for drive up the price. The average shooter probably isn't going to see any accuracy improvements with a freefloat rail system even if they have a nice scope.
Collapsible stocks seem kind of silly on 20" ARs. Losing that last ~6" doesn't seem to do much for you.
Its all suggetive really. It all depends on what you are looking for with the weapon. Go with quality parts. I suggest LMT parts kits. In the world of AR's you seriously get what you pay for. Build on the cheap, and you will have just that, a cheap rifle that will give you head aches. If you do an 18-20 inch gun, a rail system is retarded imo. On the same token, if you are not going to be using the gun while kicking in doors and blazing bad guys, a rail on an SBR is not needed. You will shoot just as good, and be able to do the same junk with regular hand guards. Your rifle will cost less as well. Sure rail systems add to the cool guy factor, but are not needed. What every you do, even if you will put optics on your blaster, pick up a good set of irons first, and use them. There is nothing as frustrating as shooting with someone whose optics went down and they can't shoot irons for ****. MASTER YOUR IRONS! That goes for everyone here.
Edit to add: The inherent inability to write swear words is really cramping my style bro.