Magpul created an update for the standard AR15 called a Masada.
It takes the best concepts from the long standing AR15 and eliminates the issues that always bugged me.
The most notable design change is that the stock no longer contains the spring tube allowing it to have many more configuration options like folding stocks and pistol grip configurations.
The second major design change is the location of the charging handle. The new location is way easier to work and is nicely ambidextrous. In fact all the controls are ambidextrous, also including the safety and mag release.
The Bushmaster ACR is the first production version of the Masada.
Toolless dis-assembly is quick and easy. You can even change the barrel fast with no tools.
--Pricey but it's now on my list.