For your son's situation, the #1 thing to me would be the potential for playing time. I would want to show up next year confident that I could compete for a starting spot.
Another factor that you didn't mention is winning. Winning is fun... at every level. Do they win conference championships? Can they compete for a shot at NCAA Regionals?
I think facilities can be important to his experience, too. A turf field in the northeast is a huge plus, for games and practice. He's also going to spend lots of time in the gym and in cages if he's a position player. Do they have to schedule time and lower a net in the gym? He'll be too busy for that.
I wouldn't put much weight on coach's personality. First, he may be gone in a year. Second, I don't think many players "like" their coach during their playing days. Coach the recruiter is usually a different guy than coach the coach (candid ones will warn you about that).
It sounds like your son is very bright, and very mature. Remind him that he's deciding between several great options. It's very unlikely that he would make a mistake with any one of them. It's also ok to go with your gut on these things. Many times you pick up on something that's hard to quantify.
Good luck.