I agree that when players are younger, Pony provides much of an advantage IMO. The field is larger and the kids learn "real" techniques. When you take a kid that has played Pony vs. LL or Cal Ripken, the Pony kids are much better prepared for their 13 yo year. However after the 13 yo year in Babe Ruth, those kids learn the skils that Pony kids already possessed, plus they get to get use to a bigger field at that time than a 13 yo pony field would provide.
I like dad10's suggestion completely. However, there are differences between leagues in various areas which can affect decisions greatly.
We're very fortunate in our area to have all three leagues to choose from with the younger kids, however at 13 there are no Pony leagues - only BR, LL, and travel.