Depends what you're looking for . . .
Are you using it as a tactical/defensive gun? You want a realistic, accurate replica of the M-16? Are you going to shoot for accuracy?
Is weight a factor? You going to add a scope?
PERSONALLY, I like the Bushmaster. I had a Colt and it was screwed up. My choice is the XM15 A2S V Match Carbine.
This is a flat-top (no carry handle) without sights for scope mounting (Redfield Tracker SE 6X - 40 mm) floated 16" 1:9 heavy barrel.
Heavy barrel reduces heat build up and barrel "whip" resulting in a more accurate gun.
Flat top lowers the height of the scope mount, so no cheek piece accessory is needed. Also, a lower mount creates fewer parallax problems with a scope.
Floated barrel adds accuracy because you're not supporting the fore end (hand grip) with the barrel and thus moving the barrel out of alignment when shooting.
30 rd mags are a dime a dozen, legal in pre or post ban guns.
I don't need a bayo lug, a flash suppressor, or even the front sight tower. It's possible to add a handle to the flat top, but I don't use one and would need to add a front sight too.
With a fixed handle upper, you can't get the rigid mount for optics like a flat top.
You can always buy a complete upper, or lower, or parts to convert.
Bushmaster seems to be leading the pack on AR production and govt. contracts.