I used to use Chiaki in the past on Steamdeck for a while, but it got problematic for me out of nowhere for no reason that I could find and I couldn't get it to reconnect.
My experience on the portal has been a lot easier and smoother, more often that not. Most especially since the update that allows for using your cell phone to authenticate into wifi that requires it. It rarely ever doesn't work now unless my PS5 or home wifi isn't working right.
As for performace quality when they're both working optimally, they're round about the same. Smooth enough for single player games that don't require the utmost reaction times. That said, even DMC5 worked well enough for me on the Portal. I could do just frame Judgement Cuts with Vergil pretty consistently. You will experience latency at some point in some fashion. No if's, ands or butts about it. So for that, I'd never recommend online competitive play on either device