I have both a Ruger PC Carbine and an FX9...
Personally, I like the FX9 more in terms of controls / ease of operation and especially ease of takedown. The FX9 has seemingly had some issues that have plagued it, but there is a limited lifetime warranty on it, and I took advantage of it and it fixed the issues (I have posted at length about those issues in other posts, so I won't resurrect them here). The weight of the FX9 I like more than the Ruger PCC (alum handguard MLOK version with extendible stock). I'm sure I may be the minority here, but aside from the uneven distribution of weight making it barrel heavy on the MLOK handguard version, the takedown is not the greatest. You need tools and the Ruger manual calls for the bolts/screws to be torqued at 65 inch-pounds (yes, that is not a typo). That caused stripping on mine.
The takedown down to the firing pin takes some time, whereas the FX9 it can be done in under 15 seconds, 10 if you are really fast. The takedown ease is important as the blowback guns really dirty up the chamber/breech/action.
For those who are used to or enjoy the AR controls, the FX9 will be welcome.
I had a couple of other PCCs before - a Keltec Sub2K Gen 2 in .40. The folding thing was a novelty that didn't last as long as I thought. But the onboard sights are terrible on it (in my opinion), the charging handle was very heavy, even years later, and the felt recoil was more pronounced (no doubt due to the weight and plasticky composition). And of course, unless you had an MCarbo offset mount (about $250), you couldn't keep an optic on there if you plan to fold it.
I also had a Kriss Vector - again, bought it due to it being different, but it was heavy, I hated that squarish/rectangular barrel shroud elephant trunk thing...didn't like the charging handle...and it couldn't run +P ammo (manual even says that). The vectoring feature is fairly useless (in my opinion) given the pistol rounds nature and it's semi-auto.
As others alluded to, the MCarbo upgrades for the PC Carbine should be strongly considered, primarily the shock buffer and c-clip upgrade. The factory one is flimsy and plastic.