I know these two can't really be compared apples to apples, but to all the knowledgeable folks here, please school me also saves me from using the search function.
I have both. Here's a quick comparison from my experience.
1. Controls - FX9 is fantastic - safety is near thumb like an AR (Ruger's safety is a crossbolt near the trigger), trigger is good on both, charging handle takes a bit to get used to on the FX9 - could be bigger. Lots of space for optics. Mag release is great - right where index finger is. The Ruger mag release is not in a great spot.
2. Weight - PC Carbine with aluminum handguard is heavy. FX9 weight is very good.
3. Takedown - PC Carbine is great - easy to take apart into two for stowing away / backpacking. This is probably one of the best features about it - the takedown into two pieces.
4. Disassembly and Cleaning - advantage to the FX9 all the way. Two pins and everything comes out. Very easy to clean. But FX9 gets dirty fast. PC Carbine - you need some hex tools. More involved steps to disassemble. Bolt assembly - recoil rod and especially the shock buffer somewhat annoying to take apart, and then there is the bolt itself with two pins for the bolt face and a pin on the side for the extractor. Shock buffer and clip is really annoying - cheaply made and goes out of alignment, causing issues with trigger assembly aligning for pins. The two hex screws / bolts (under front of receiver, the one that screws in the grip) - one of them is starting to strip. They are "captive" or whatever, so they don't come out all the way.
5. Accuracy - hardly scientific and I am not a great shooter, but out of the box, the FX9 is more accurate. I know others will disagree. I use the same red dot sight on both guns.
6. Ammo - FX9 documents say to use 115gr to start. FO told me there is no break in period. FX9 should not use aluminum ammo according to the documents. Others have indicated FX9 is ammo picky. I have shot 115, 124 and my usual 147. No issues. The PC Carbine has eaten everything without issues
7. Last round bolt hold open. My PC carbine does not like Glock mags - the bolt hold open consistently does not work with those. Similarly FX9 has some issue with Glock mags, though it didn't at first. Magpul PMAGs and ProMags no issue
8. How it comes from the factory - the FX9 is bone dry. Lube it. Ruger PC Carbine came generously lubricated.
9. Looks - personally I think the FX9 is a better looking gun
10. Price - about the same. For me the PC Carbine with adjustable stock and aluminum handguard was 1149.99 + tax. The FX9 was 1349.99 + tax.
11. Overall enjoyment - for me, it's the FX9.
12. Other - the PC Carbine comes with a SR9/S9 magwell and magazine but also comes with a Glock magwell (no magazine). The FX9 (at least mine) didn't come factory with any Glock magazines but the retailer added one. Both guns accept Glock 17 and 19 mags.
13. Other - Part II - the bolt lock for the FX9 seems to release with jolts or movement intermittently. The Ruger PC Carbine one stays put until manually engaged.