In the same boat and have been doing a ton of research. Here's the feedback I've found:
FX9
Pros:
- one of the better looking carbines
- "AR" parts avail, but otherwise solid out of the box
- good ergos
Cons:
- requires more break in period, and initial maintenance and tweaking before it gets right
- more prone to jams if not using OEM glock mags
PC9
Pros:
- huge aftermarket for Ruger
- shoots out of the box
Cons:
- can require many upgrades to get "right" (mcarbo etc.)
- heavy
- worse ergos (mag release etc.)
doodle jump
Personally still deciding between the two, but leaning toward Ruger for "tried and true".