Best has to be my first, in 1946, which was returning from the Isle of Man to Speke in a DH Rapide, having gone there in the ferry from Fleetwood in rough weather.
Worst was probably in the 1980s in a MAS F27 which was just out of Kuala Lumpur when the cabin temperature rose alarmingly and reaching for the punkah louvre, I found it too hot to touch. Captain Speaking announced there was trouble with one a/c system and he would have to shut down the engine and return. That he did, but it was his high-rate turn into the dead engine that frightened me most and made that the worst flight.
Or perhaps it was the Royal Air Nepal flight from Kathmandu to Delhi where we had a fellow-passenger dressed in battle fatigues who had regaled the departure lounge with a tirade about his beliefs and how he had studied war, etc. etc. to the point that he was so obviously the hijacker that the rest of us were reluctant to board. When we did we made sure we sat where we could keep an eye on him and on arrival at Delhi made sure we were through immigration before he was.
Since it turned out that he wasn't the hijacker I suppose the flight wasn't too bad really.