should I play the one inside celeste or the one on itch.io?

i recommend you play on the standalones provided under resources (download the one for whatever os youre running), as these come with the pracitce mod too and allow you to disable screenshake. playing on web is not preferable, but definitely a possibility, just adds some input lag. the version inside 2018 celeste got recently updated to be more accurate to the p8 version, so that works too.
id recommend standalones as they are most accurate to the actual pico8 version, and look best for recording.