We flew to Isla Mujeres using the Jet Blue Airlines and we do recommend their services. The plane was on time, everyone had a lot of space for legs, the flight attendands were really nice and the airline offered free drinks and snacks during the flight.
One has to remember that they charge for the bags. If you pay for the bags on line, the price is 20$ for one bag if you do it at the airport, it is 25$ for a bag.