[mavrick0]

For me it's lipo. They hold a better charge, take a charge better and don't form a memory like nimh batteries do. But if you are using lipo's you need to either have an ESC with a lipo cutoff built into it or use a lipo alarm so you don't over discharge them and damage the pack. As for the sort of lipo really you only need to deal with a 2s(7.4v) battery in a king hauler and the nice thing with the king having a nice flat battery holder you aren't limited to a special type of lipo like you would in a truck like a knight hauler that the battery holder is in the same shape of a standard nimh battery.