What are the advantages the AK-47 has over the M4 carbine and the M16A4 rifle, and vice versa?

Also, what are the advantages of other weapons [HK416; HK417; MP7; .50 Beowulf; SCAR; Magpul Masada; Bushmaster ACR; Kris submachine gun; XM8; Barrett REC7; LWRC M6; IMI TAVOR; etc.] over each other? Out of all of the major ault rifles, which do YOU think is the best for military use? Finally, what factors make an ault rifle a "good" ault rifle [rapid fire, range, accuracy, reliability, etc.]?