Since the start of the war I've never forgotten the picture of a US Spec OPs Solider that I saw. He was bearded with turban to fit in and he had an AK in hand, a chest full of AK mags and a M4 slung off his back.
We long ago should have adopted some type of modular weapon systems that could be adapted to particular warfare environments. While 5.56 provided the ability to carry more ammo, and improve accuracy in a certain environments such as the jungles of SE Asia, the M4 is often at a disadvantage where any type of hard cover is concerned. The AK47 is often able to penetrate certain types of cover that a light 5.56 load may not. Unfortunately, while fairly bulletproof, the semiauto AK's I have personally spent time with were not much to brag about as far as accuracy goes.
If I had to trust my life to one rifle it would be the LWRCi M6A3.