This is all personal opinion, of course, and no two viewers will agree absolutely. My best (Michael Strogoff) and worst (Brute Island) are both comparatively obscure so don’t be shy if your choice is equally unknown. On the other hand, don’t be afraid to let your flag fly for famous movies like Battleship Potemkin or The General. We’re all here to share and have fun.
Feel free to only answer for either best or worst. No one says you have to share both. This isn’t the Spanish Inquisition. (I feel a Monty Python quote coming on!)