I like 4xBB personally

99% of the time when I raise preflop, It's exactly 4xBB ...

also, when you hit with your AK, a $4pot doesnt give you much to raise in... if the pot is $12 you have a much better chance of actually making good money with the hand.

Hitting your hand on with a $4 pot isnt going to even come close to the profit you will make with the exact same situatuion with a $12 pot.