The best advice I could give about the AR-15 is to buy a used one in just about any format that suits your fancy, and in a brand that will keep a good resale value (buying an AR-15 used then selling it for the same price a year later isn't uncommon), the once you're familiar with the system, sell the factory jobber and build your own. You'll learn what you need/want out of an AR after a few short months with one of your own, and once you see how easy they are to build, you'll be able to REALLY save yourself some money on a home brew. The only thing I worry about being "top shelf quality" for AR's are the barrels and triggers, the rest, you can skimp on or splurge for depending on your own personal taste. In general you can build a top of the line AR-15 for about the same price as you'd pay new for a factory "standard" model, depending on how fancy you get with all of your components (thoseTiNi coated bolt carriers set me back a lot, but dang they look good).
Like others have mentioned, you really need a direction for your weapon before you choose which AR to get. Are you wanting some tricked out "tacticool" marvel, or a barebones "strictly stock"? Are you looking for high volume shooting, or precision work? Hunting big game, or small game, or just beer cans?
One thing that I enjoy the most out of any AR, and what I wish I had on all of mine, is custom paint. Black rifles all look the same, but I tell you, the first time I saw an AR-15 sporting a snow camo dip job, it sure caught my attention!