As referenced by WAFP, unless things have changed you don't find out if you have a pilot slot until the spring of your junior year, which is after you have committed. Nothing says those slots can't be taken away by the needs of the service as in the early 90s. Might even be due to political / $ constraints - reference the upcoming change of administration. My point is to pick a branch of service that you would be happy in, even if you do not end up with a pilot slot, because lots of things could happen between now and earning your wings.

Good luck