Off the top of my head, a few might change if I were given a comprehensive list of each decade. :)

20s: NOSFERATU
30s: THE MUMMY (but Lugosi's DRACULA for performance)
40s: THE BODY SNATCHER
50s: (tie): GOIJRA (Japanese version)/NIGHT OF THE DEMON
60s: (tie): CITY OF THE DEAD/THE BIRDS
70s: THEATER OF BLOOD (you said favorite, not "best"!)
80s: FRIGHT NIGHT
90s, 00s: No selection - just not that gaga over anything put out

Jim N