U.S. Rio Bars Specialist: Ashton or Madison?

Hi All - this is assuming that the U.S. takes a bars specialist --- and you never know with Marta! But if they do, who do you think it should be? Who is better, Ashton or Madison? (This is assuming that neither is injured).

I think I would go with Madison, but I'm interested to hear what others think. Madison can be a solid backup on all other events, in case of emergency, whereas Ashton can only do bars and beam. Also, I kind of feel like if all things are equal, the nod should go to Madison as (one of) the reigning WCs on bars).

Thoughts?

U.S. Rio Bars Specialist: Ashton or Madison?