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.

So... not through the lexaloffle bbs?

That's how I usually run

BBS/web is fine, one of the 1:37 runs on the boards was done on web, it can add some input lag though

the game has the least input lag on the celeste 2018 and standalone version.

I believe pico 8 console has 1 frame of lag, and i'm not sure how much bbs and web has but it's not too bad.

I run the game on pico 8 with 1 frame of lag and so ultimately as long as you don't drop frames you should be good no matter what

for practice you can you pico 8 mods or webek online and well web also works fine.