I have no idea what the best is, but my 2003 came with a SuperChips MicroTuner, that has a diagnostic readout of codes and faults and a handbook for the same... It as well has three stages of chip up, Stage I is reported to improve fuel economy 1-2 mpg from reliable sources of mine towing big vans in the Outback, and Stage II and III are for the throttle jockeys that can be hard on tranmissions and such but a lot of fun from reports... My own Ford, the 2003, has a new transmission from the previous owner probably playing too hard.. His bad luck, my good luck...
Anyways you might try them on their website as you get the dianostics plus three stage chip up..
Regards from the Lone Ranger in Australia