I did ROTC and became a lieutenant, and accepted an additional duty service obligation to increase my chances of being branched Aviaiton- my gamble (and hard work in college) paid off and I got Aviation. Then I did well in primary, instruments, and basic warfighting skills (the beginning of flight school) and got to be third or fourth in my class (of mixed officers and warrant officers) to pick which airframe I wanted out of the available ones, and chose Apache. Not that my OML mattered; after I went, all the blackhawks were taken before the Apaches, so a couple people who didn't want to fly Apaches had to.

If you don't want to go to college yet and/or you want to fly more than you want to tell people what to do, I'd go the warrant officer route. It's all a bit competative, but not nearly as competative as fighter jet.