they all do the same damage in the end
I personally prefer ice because then I can usually tell how the fight will go since all my hits should remove about the same % of his lifebar
lightning is more iffy, you might end up beating a monster you otherwise couldn't if all your rolls come out high
or you could end up losing because all your rolls are low
basically the best charm is the one with the most EE that you can buy for the least amount of fg