TOS - Honestly, probably one of the cheesy episodes like The Way to Eden
TNG - Remember Me, I like the premise and that it’s a Crusher episode
DS9 - Bar Association, still as relevant as ever plus it’s got the Ferengi in it which is always fun
VOY - Let’s not kid ourselves, it’s Threshold
LDS - I, Excretus, I really like Boimler not only passing a test designed to be impossible but refusing to accept anything less than a perfect score
Everything else I either haven’t watched, watched too recently to have a comfort episode yet, or is too story driven for one episode to stand out over the rest