In the list you provided, the order of quility goes:
Rock
DPMS
Bushmaster
I've owned all of them, no major complaints...I did change things like triggers, but overall any of them will please the first time AR owner.
Like snort says tho, AR guys normally have them built to their likes/application and will often own many set ups..or at least many different uppers, as they are as modular as they come, and have so many options...but IMO, until you own one and use it, you wont know what specialty items you will prefer.