A320/737
To be honest, I doubt anyone knows what JET BLUE is looking for or anyone else for that matter. I mean geez, I got hired by PBA when I was 19 years old, who would have thought I could get hired by someone at 19 with less than 2000 hours and 400 hours pic in a C310.
HOWEVER, I would still suggest getting the 737 type and going from there. Too any US Air, NWA UAL guys with time in the plane, regardless of the seat, to compete with for Jet Blue and USA 3000. If you really get desparate go to AWA or Air Tran.