Now.....the other factor concerns Marines.....
They are an entire phenomenon all together and everything I just said throw out the window.
Every single Marine Officer, be they USNA, ROTC, OCS, has to experience The Basic School (TBS) where they are molded into the Marine mindset the MARINES WAY! And in my talking with Marines who came from all 3 ways to their 2/Lt Commission ------no one cares one whit about your prior education. It's what you do as a M A R I N E that matters, and that happens from second one of TBS down at Quantico. My girl will take this path and sometimes she actually whistfully looks at her Marine ROTC component friends who have already had many many trainings with the Marines while she is pretty much all Navy-scheduled for Summer training requirements that conflict with her Marine-heart. But that is the way it is for USNA interested Marines. And they too must suck it up until Service Selection, Commissioning and that trip down to Quantico.
Frankly whatever path your son chooses will prepare him well. May God guide his decisions.
An interesting stat I stumbled across for USMC Commissioning Sources FY-07 are as follows:
OCC-33%
PLC-24%
NROTC-16%
USNA-14%
MECEP-8%
ECP/MCP-5%