Might be fun to have both as they can use the same magazines and ammo, it's easier to equip yourself and a buddy for a fun range day or to just keep it interesting and different for yourself.
I have an FX-9 and my father has the PC9 - we've determined that the FX-9 is definitely faster in target transitions and reloading, overall the accuracy is about the same, and you're going to have a pile of fun either way. I've enjoying putting some work into my FX-9 as well, but that's not for everybody. I've never been a "just keep it stock since that's how it's designed and that's the way it's meant to be" kind of shooter. I don't own a single firearm that I haven't at least changed the sights on. Having said that, this is kind of the Honda Civic of PCCs in that you can swap out just about everything until you have it perfect for you on the base chassis.
I've done the trigger (TriggerTech FX-9 adjustable trigger) added a TechWell magwell, changed the stock to a Magpul CTR, the grip to a Magpul MOE, added a QD point up front and a sling, the buffer is now an H3 and there's about $1.50 in quarters in the buffer tube to tighten it up a bit, some picatinny for a light when I want to chuck it on there, some grip pads on the MLOK, and both a Vortex Venom and some Magpul BUIS to complete the first iteration of my tinkering. I may change out the Vortex to something else later on, and same with the BUIS, but it works great how it is now so we'll see if I get bored and frisky later! I'm still playing with the buffer and spring system to tune it the way I like it the best, so that's been kind of a fun process too.
I've found SGM 10/33 magazines to work the best in it, OEM Glock, Magpul and a random (unsure of brand) magazine don't always engage the LRBHO. Haven't tried ETS mags yet, but will eventually as I've heard they're good too. It totally eats all the ammo I've fed it (no aluminum case) regardless of 115, 124, or 147 grain. I "broke it in" on 115 grain though with the stock buffer and spring just to follow the manufacturer's recommendation.