A few comments and thoughts after reading this board for 8 years....
The Hamptons League is a rather new league (son was supposed to play there this summer but didn't due to surgery). Can't beat the venue. But, as for spring-boarding to the Cape, I think that would more fit the New England Collegiate Baseball League (NECBL), especially for pitchers.
Coworker's son played for the Alaskan League. Her major regret was not going to see him play there. (Tried to get keewarson to consider it so I would have a reason to visit, but he didn't buy it.)
After the Cape topped at #1, I think Northwoods is next in rank. The Cape is non-profit and Northwoods is for profit. From what I have read, Northwoods is most like playing for the MiLB, with a long season. Heavily scouted like the Cape, and very well attended by fans. They recently broke an attendance record of 1 million this season. I understand if one of the teams goes up for sale in the NW league, they can sell for over a million.
Then there are a host of other leagues. Most leagues charge something ($250-$500-$750) ....except I believe the Valley League, but Hokieone can clarify. Then there are the pay-to-play leagues: there is thread on here regarding Myrtle Beach. Worth reading if your son decides to head that way.
New teams pop up. Charlottesville (VA) Tom Sox in the Valley League comes to mind as a more recently formed team just this past summer. Wonder if new team expansions could be due to a need since American Legion changed their age structure?
Your son doesn't get to choose where to go, the college coach will place his players. Even if several teams show interest in your son, it is still ultimately the coach's decision. Some players will know in August where they are headed next summer, and some in May after the college season has ended.