Also, experiences aside, do you want to use an extra year of your life at prep school to end up in the same place (a Navy commission)? Avg life expectancy being 72 or so, you've committed 1/72 of a suicide. Just a little philosophy, borrowed liberally from alt-icon Henry Rollins.
There are pros and cons of each. I tend to think that a civilian school gives back what you put into it, i.e. half-ass it and give 0.25, you get .25 out. On the flip-side, give $1.50, it has a lot more diverse opportunites to give more back. The academies give almost everyone the same dollar up their keister a nickel at a time.