Elmira/Corning Regional Airport. User-friendly, convenient and quaint.

Honorable mention goes to BTV, Burlington, Vermont. While I think it just breaks the five-gate threshold, it's a quirky building that seems to have been patched together from about five different architectural eras. Plus, the airport authority converted the old control tower on the roof to an open-access observation tower, complete with piped-in ATC audio! Great place to kill an hour waiting for a flight