Board Thread:General Discussion/@comment-1841650-20131216160717/@comment-2164259-20131218111945

Souls have passive effects that last even when they expire, they are stronger than all the other powers but they dissolve very quickly and can't be levelled up

Kenshins have the strongest power, but they use a lot of GP compared to the others and can be broken through easily with other Kenshins

Kenshin armed dissolve quickly (not as bad as Souls), grant you extra passive powers (especially speed) and break through Kenshins easily, but also consume GP immensely

Mixi-maxes just give you a straight stat upgrade + two more hissatsus (plus now you gotta choose beforehand the few players who can use them)

I think even considering that they got nerfed in Galaxy, Mixi-maxes are the "best" powers, as in the ones with the least drawbacks.