i think after season 11 - there was still some life in the show at the point and it would've ended perfectly with behind the laughter.

seasons 10 and 11 are a lot worse than i remember (season 11 not as bad), but there are several moments worth saving and enough satisfying episodes in the mix. after that you have 1 or 0 good episodes per season, none particularly worth saving (except trilogy of error, but season 12 is pretty bad even for mike scully and simpson tall tales would've ended the series on a rubbish note).