My favorite, and I think the best, is Bela Lugosi. Probably because of a combination of how old I was when I saw it the first time and the fact that it was the first Dracula movie I ever saw. Plus I have to admit that when I read the book, Lugosi was the image I had in my head while reading it so everyone after that just paled by comparison. That was one scary book!
My favorite silly Dracula is George Hamilton in Love at First Bite.
There are so many bad versions of Dracula it's hard to say who I think is the very worst.