The AR15 platform is available in a wide variety of models, styles and applications. Now if your asking who, what, which one, then you will hear all kinds of feedback.
Obviously the big name brands will be exceptional rifles. But a lot of the folks here have taken some seasoned advice from others and built no-name rifles for themselves with excellent results. Others have scoured around and found great deals on complete rifles from very good manufacturers. Dig around the AR threads and you will find a wealth of info, try to dial in what you want and come back. This way you can get more specific info.