That's a good one, and yes, it's hard to pick one out of so many. I'm only up to S8 on rewatch, but two that have always stuck out for me are the loop one Window Of Opportunity
(where O'Neill and Teal'c have to relive same day; I love
causality eps like TNGs 'Cause & Effect') and Wormhole X-Treme
, just 'cause it's a great meta episode for such a popular franchise. They're not necessarily the best, or indeed my favourites (though I like them), just really distinctive.