A Mac series (MAC 10, M-11, M-12 etc) is basically a room-broom. A high rate-of-fire subgun that fires a pistol caliber cartridge.
The AK series is a true assault rifle that fires an intermediate cartridge (7.62x39, 5.45x39 etc). The AK series is physically larger (most variants) than the MAC series.
There are quite a few websites dedicated to each series of firearm on the 'net.