So much good PARENTING advice above. You def have to get to the root of his indecision.
Can you try to get a little extra time by scheduling a visit to the HA a little later in September? You have to come a long way, he might understand. I would normally agree with Smitty and JCG about going with the best pedigree, EXCEPT if he plans to do something where a graduate degree is in order. Applying to grad school with a 2.5 is like baseball recruiting with an 82mph fastball even with an elite school's name at the top of the transcript. And grinding both in baseball and in school to get a decent class rank might make life unpleasant for four years. Unless he enjoys the grind itself, he has 40 years to do that.
Ultimately you have to know your kid and his personality. If you think he is comfortable with the intensity of the more academic schools, then encourage him to go! My best friend has a non-baseball playing kid same age (sometimes I forget those exist), he and Lefty have grown up together. He is a National Merit Scholar, 35ACT, all APs and two B+ on his transcripts, with a carefully crafted (by mom) list of extra curriculars. In other words a viable candidate at most prestigious schools, but he won't be applying to them. He wants to enjoy his college experience and the intensity at some of these schools is a total turnoff to him. So he will likely head to a "good" school that is less prestigious and have a lovely college experience.
We often talk about 4 for 40 here, using 4 years of baseball to set you up for a 40year career. Don't forget to consider how graduating from "X" university will be a help (or hindered) as Cade tries to get internships, grad school, or a job with whatever network each of these schools has.
I wonder if you might get some extra insight into why he won't pull the trigger if you were to ask him what HE thinks your older two should have done differently? some insight into what he's trying to avoid...
Also, you have raised THREE wildly successful kids! Kudos!