the Maiden machine has great art package possibilities. Whether you're a Maiden fan or not I think most can agree the artwork is very colorful and done very well. There would also be a lot of "toy" possibilities.
KISS could have a lot of potential as well but Simmons and Stanley will not allow merchandise to be produced unless it depicts its current line up only! I am not a KISS fan but I think back over the years of all the different members (i.e. Carr and Vincent) and think it would be neat to see a "KISStory" machine that includes all of the members on it.
Either machine would have a lot of potential for both artwork, "toys" as well as rule sets.