I believe in my heart and soul the 300BLK is the shitz. From "barely .22LR" to "slightly exceeding the energy of the AK cartridge" that one caliber has one covered.

The downside; it retains what I (personally) perceive of as the weaknesses inherent in the AR platform. Until those issues are fixed; I'll continue to shoot the crap out of my 300BLK, but I'm not letting go of my AK. I'll keep training/practicing for proficiency with both arms.