Half of this thread is pointless, the worst MD is/was/forever will be Charles Horton. No fathomable understanding of how he originally became an MD and how he became one again after Connex...
As to best I've heard that Tim Clarke of Anglia was meant to be fairly well liked. Personally I quite liked Ruud Hacket on AGA.
Tim Clarke, AKA the poison dwarf. I'm glad someone mentioned Tim Shoveller. Hard working and enthusiastic were his claims to fame. Also happy to accept what went wrong was his responsibility - a rare thing nowadays.