Ka-50 is better than Mi-28. Russian tests of both machines certified it. Although Mi-28 has more roles; it can carry or rescue limited number of soldiers, it has further range and it is "more" multirole. Ka-50 is an elite anti tank/vehicle destroyer and the better punch for special operations. The main problem with Ka-50 is its high monetary value and the need of elite pilots to manage it. That is the main reason Ka-50 is used for special operations while Mi-28 is the main attack helicopter.
Small, fast, and agile, high survivality helicopter, the better choice for fast hit and run attacks in the face of the enemy.