I know there is a thread on here somewhere about this but the short answer is: only if you have a medical problem do you go from jets or props to helos. Going from helos to props, or going from helos and props to jets is limited to a few slots every year (chances are akin to winning the lottery) and only happen after you have done a fleet tour (i.e. - 3 to 6 years). Once again, the slots are EXTREMELY competitive so whatever aircraft you select in flight school is probably the one you will fly for your career.
Good Luck.
(One big exception to this is if you leave active duty, you could be re-trained on virtually anything in the reserves.)