Best actor, hands down, is Johnny Depp.
I consider someone is a good actor by the variety of roles they play and their ability to bring depth to that role. Depp is excellent as this. Most actors only play the same guy in different circumstances. Come on, is there really any differece between Arnold as Terminator and Arnold as just about anyone else? Tom Hanks is great, he really is, but he always plays the 'everyman' role, sort of like Jimmy Stewart.
Depp is anything but an 'everyman' and yet he brings humor, pathos, intelligence, humanity to every role he plays from a pirate to Edward Scissorhands. After my 8 year old watched Charlie and the Chocolate Factory, he commented that the movie was funny, but that he really felt sorry for Charlie. And, that was because, for all the bizarreness, Depp made us aware of what a sad person Charlie really is, and that sadness was something the Dahl had in the book, that we didn't see in Gene Wilder.