I disagree with Bosco, there is a Best. Not what that "Best" is... I don't know. And there is certainly a "Best" for your requirements.
I believe Daniel Defense builds the best carbine around. First and foremost they are a manufacturer, it wouldnt matter if they were building guns or turbine engines, they have expensive equipment, trained employees, and a process that is second to none for quality control and sustainable manufacturability.
I would say a list of the top brands include DD, LMT, BCM, and Noveske.
Of course not all of these manufacturers "Build" everything. For instance, Noveske does not manufacture barrels, FN does for them. Where as DD owns a cold hammer forge. But may not make some of the other components of the carbine.
You will be happy with any top name brand.
Talk to Jason at Pelican Firearms, he has ridiculously low prices and a broad selection.
+1 on DD. I have the DD M4V7. It's also the only AR I have so I am both ignorant and inexperience on anything else. I love it so far though.
Goteron, what is your opinion of LWRC? Namely, their personal carbine? There was a spread on it in AR15 magazine a few months back. Due to no time/spare income I'm in dream mode and really like the look of it on paper. Do you have any experience with the brand or that particular model?