Being the pedantic sod that I am , AK has the longest timeframe (September 1940 to May 1945) and the greater variety of terrain (desert to mountain and all points in between). It may have a greater range of equipment and it certainly offers more national armies.
However, 'BB is the more popular CM version for whatever reasons. I just hope that we get an AK version because that would open up so many possibilities for manoeuvre battles that only the desert can truly provide