This has been discussed over and over but the short version is:
Go to Primary: unless you graduate #1, it depends upon the needs of the Corps, your grades, and your preference - in that order.
This determines jets, props, helos.
Advanced is the same (whether jet advanced or helo advanced) as above: needs of the Corps, your grades, and your preference - in that order.
This determines which specific jet or helo you get (only 1 prop - the C-130)