So I decided to try an experiment with today's video and upload a video in my screen's native resolution of 1440x900, a 16:10 aspect ratio.
Whereas both platforms support the 16:10 aspect ratio, YouTube insists on stuffing it into it's 720p re-encoded resolution making it look sub-par to its #PeerTube counterpart.
Basically, PeerTube seems to have better support for slightly odd resolutions. A small thing but interesting nevertheless.