What are your hopes for playing in college? Do you see yourself playing DI, DII, DIII or NAIA? Be honest about the last question, do you really have the dedication and skill set to play DI or DII. If you answer yes, play 16u and write every coach of a school you want to play for.
If you are a DIII or NAIA player (not necessarily because of skill, but because you're going to college for an education and not to play ball) than I would look seriously at 18u.
JMHO