If that and Mitty are your choices, I don't think you can make much of a mistake either academically or athletically. Certainly, the Mitty coach has a terrific reputation that sounds like it is very well deserved. But again, the quality of the competition just to make the team and/or play in the WCAL school is likely to be quite different.
Seems like you and your son are looking at very nice options. While your son's baseball experience will be somewhat different at each, if he is successful, they both provide options at the end that are quite equal.
If it makes any difference to you, our son went to a small private school. During the summer he played SS alongside the 3B from a WCAL school who was the a CCS first team selection. They both had options after high school and both developed baseball wise pretty equally over the years they played legion ball together.
Good luck to your son in baseball and with his options.