Which cheese molds first?

Answer 1

That would depend upon the conditions that exist, the quality of the cheeses, the presence of anti-fungals, etc.

American has been processed and probably heat-treated. The Swiss you are referring to might be natural, though there is processed Swiss. I'd vote for the natural going moldy first, but this sounds like a good science experiment.

Answer 2

Swiss cheese takes the longest to mold

Answer 3

the yellow one