What should we call folks who are in Starfleet? Folks in the army are called soldiers, folks in the air force are called airmen, in the navy they're sailors, and don't call a marine anything other than a marine. Even in the coast guard they're guardsmen!
So, what the heck should we call folks in Starfleet? Crewmen? Explorers? Starfleeters? Starfleet officers is most commonly heard in canon (even when referring to Chief O'Brien), but that doesn't begin to cover everyone in Starfleet.