My favorite episode is "The Giant Gila Monster". This one has it all. Hot rods, bad songs,(I sing whenever I sing whenever I sing), a French chick, cheezy miniature sets and an unending series of "leg up" poses. Also great host segments. Frank beating up the Renaissance Festival punching bags is my favorite of the bunch.
Daddy-O always keeps me rolling, escpecially with the button malfunction at the end. Rocketship X-M, Sidehackers, Wild Rebels, Hellcats, and Godzilla vs. Megalon are also all great. Really just about anything from the first four seasons is good stuff (save Manos of course).
As for the worst, take your pick from any SciFi Channel episode. Nothing was funny about that Pearl Forrester. The movie segments were pretty good, but she was just so annoying I wanted to put a brick through the screen.
Definitely Catalina Caper, I just love the Ode to the Creepy Girl!
Rocketship X-M is good, and so is Teenage Caveman (Roger Corman just had to make this list.) I've actually seen this one available at video stores (NOT MST3K-ed) Don't know if I could sit through it in its natural state.
How about Teenagers From Outer Space. The only way I'd sit through that one, unMiSTed, is...
WITH TORTURE!