A lot of good stuff here, but three pages in, and no one has asked "Whatcha gonna do with it?"
It's less the brand name, than the features you need. So far everyone has said, Ok, you need a truck, buy Brand X. Well, what's the truck going to do? Makes a huge difference. Look good in the driveway? Haul cattle in a headache box? Trailer your boat to the lake? 4 wheel into the back of the property and haul firewood out?
General features you probably need, pros and cons:
Barrel - what type ammo means the twist, and how often means whether to get chromed or stainless. Chrome is high heat erosion resistant, but not precision, 2 MOA is milspec. Stainless is more accurate, but not common in a lightweight profile.
Use a full auto M16 bolt carrier, the weight works to help cycling, the cutaway bolts get too light. Use an MPI bolt, it's been individually checked.
Just about any lower and upper will do, how the upper was assembled can make some small differences, it still goes back to how good is the barrel. The A3 flattop is better for mounting scopes.
Handguards or a free float is always a warm discussion, what free float fans won't admit is that the barrel is still the final accuracy control. A free float just keeps the sling or hand pressure from affecting the barrels point of aim, it cannot and will not make the barrel more accurate than it is. Again, milspec is 2MOA, with handguards, that's a 8" circle at 400 yards, and a lot of folks are hard pressed to do it. It would still be a good heart/lung shot hunting. We sometimes get hung up on the bling and forget the application.
After that, fixed stocks do the job, most people never wear armor vests, if you do, you know what you need. For the rest of us, almost everything else is bling, makes no contribution to accuracy, or helps the shooter. The Army and Marines have not changed completely over to the M4, M16's are still the primary individual weapon, and the Marines are sticking with them, now issuing the M16A4. They do add an ambidextrous control.
If you get a 16" barrel, get midlength gas. Don't use surplus or used GI mags, buy Pmags from Magpul, they are much more reliable and abuse resistant. Most used aluminum mags should be crushed, not resold to be someone else's problem child, but that's what all those otherwise responsible shooters really do.
Specify the way you plan to use it, select the features that match, and then worry about brand fans telling each other how wrong they are. It's funny, since there are less than half a dozen receiver forgers anyway, they all work to meet milspec and machine each others stuff. Colt does not forge their stuff, either.
At that point, the price difference should really be questioned, especially when the premium to have a scratch free rifle lasts about the first range trip.
WB