I'm fortunate to have acquired a 2016 Fender Jazz Elite IV earlier this year and very recently picked up a 2017 Sonic Grey, Fender Pro Jazz. I put a set of TI J344 Flats on the Elite a few months ago and the Pro came with a set of rounds which still sound new and bright, at least for now but eventually the rounds will need to be replaced but the TI flats will probably out live me. Which bass would you use for the flat strings and why? They are both a Fender Jazz but there are some key differences such as the Elite has an active preamp, jumbo frets and noiseless (version #4) pups, while the Pro is passive with tall narrow frets and their newly designed alnico pups. I'd like to keep one with rounds and the other with flats. But which one should get the flats or rounds? Which type of string would you use on which bass and why?