Once you get to flight school and get your rotary wing license, you will be assigned an airframe. Sometimes there is a choice among them all, sometimes the needs of the Army trump that and everyone in a class is assigned a particular airframe.
After your initial assignment, there is a chance to fly fixed wing, but it is very limited. This will either be leer or Gulf Stream jets for VIPs or surveillance aircraft.
The ability to cross to a different service at graduation is very limited. Don't count on it. In fact if you really want to fly jets/cargo planes and have a choice of West Point or reapply another year to Air Force or Navy, you should turn down West Point and try again for one of the other SA. Don't ignore Coast Guard as they do a lot of flying as well AND Merchant Marine allows you to commission into any service.
Additionally, be mindful of what you ask for. The AF Fighter community is seeing their flight hours cut drastically and a focus on diverse experiences (ie non-flying jobs) right now. You need to talk to some of the current officers in that service both junior ones to see what experience you will have and senior ones if possible about what they forecast for the future.