We prefer to fly into/ out of Orlando (MCO) for plentiful direct flights, good services and good prices. My parents are joining us in February, and preferred West Palm (PBI), as it was only about a $50 difference (including car rental and airfare) for them. PBI is a smaller, somewhat easier airport, and much fewer crowds.
Melbourne is closest, and having done both MCO and PBI, I'd say the drive is almost exactly the same in terms of time (remember that the resort is actually north of Vero Beach proper, in Wabasso, closer to Sebastian).
Good luck!