The best thing about owning even a moderate quality AR15 is the ability to accessorize and build upon the platform. If you've got a good well built AR15 Lower, all you need is the skill to know how each variation of the AR15 family of firearms can be used. A Standard A2 model is a great starting point for learning the basics of shooting. Spikes Tactical Uppers You can turn a target model AR15 into a CQB weapon but popping out 2 pins and swapping in CMMG Uppers or even changing calibers to the Smith & Wesson 5.45x39 upper. With ammo pricings being what they are a 5.45x39 upper from S&W will pay for itself after 2 or 3 thousand rounds. All CMMG Uppers are complete with bolt and bolt carrier group. Be sure to check out flip up front and rear sight options while you are selecting your uppers.
The piston driven LWRC uppers are more expensive in some regards, but we have seen fewer parts breakages with long term use and there is now a new light weight AR15 upper that is less expensive.