What is the feature of the pic we are looking for. The CPU SPEED (8bit or 16bit...), the SRAM, timers?

its not my project I don't know what you have planned but generally speaking if you are dealing with parsing strings from a serial stream , more sram is better ,the possibility of more speed is always better. make sure there is plenty of flash space to hold the program. if its a one off project get the best chip with enough pins and features required .
if you are going to do large amounts of and/or complex math then pic18's with a hardware multiplier can increase speed and
reduce code size

pk2 will program 18fk22 series , once you have used a chip with pps there is no going back. the k42 series chips leave the others in the dust