You know - from testing it, you can lvl up a girl up to lvl 40 just using ampys at a pretty solid rate. Saving up on a lot of money in the process.
After that they give good exp only if they are the same type as the girl.
Thats how I lvled up Soapworth on my DMM account, 1-40 approx, then manyus, then evolution, then ampys again, then manyus, then blooming then ampys again