I bought a Glock 22 (.40) for production. If I did it again, I'd buy the 9mm. Primary reason I went for the .40 was because I didn't have to buy a new set of dies and could just change things over from my standard gun.
Dumb...after I change the powder measure, and adjust the seating die to the new height (I use a Redding competition seating die, so it's easy to switch it back and forth between 2 settings), it's still almost as easy to just switch out to a new toolhead/shellplate.
My next production gun will definitely be a 9mm.