Welcome Twins,
I'm not sure what purpose you are looking for the new AR15. If its just basic target practice and defense, the A2 configurations are a good choice. Basically the A2 configuration has the carrying handle on it. You can get varing barrel lengths from 14.5inches with an extended muzzle brake, 16inch, or 20inch barrel. My preference for balance, velocity, and length is the 16inch barrel.
The A2s as opposed to the flattops don't offer as many sight options, but you will always have iron sights that will never fall off or become lose under normal circumstances. If you get a flattop you have to add pop up rear iron sight or removable carrying handle with sight on it.
As for brands and cost most people would agree with me here when I recommend Bushmaster, Armalite, and Rock River Arms as the tops. Olympic and DPMS brands are also to be considered. For a 16inch Bushmaster Carbine with carrying handle you should be able to get one for about $700.00 easy. Armalite around $800.00 (lifetime warranty is included), Rock River Arms I believe $700-$750, and Olympic around $650.00.
For the money, reliability, customer service, and having a chromelined barrel and chamber the Bushmasters are hard to beat.
There is so much more information do some searches on the industry forums.
No Slack!