The First Edition of Best Actor is in 1940:
Oscar Nominees (My Ranking):
1. James Stewart - The Philadelphia Story
2. Charles Chaplin - The Great Dictator
3. Laurence Olivier - Rebecca
4. Raymond Massey - Abe Lllincoln
5. Henry Fonda - Grapes of Wrath
A weeker than usual year for actors, James Stewart made a fine performance but not anything groundbreaking. I usually love Laurence Oliviers performance, but this was not his strongest performance. Charles Chaplin is the only one who gives a memorable performance you remember in the 21st Century, but I think Jimmy was better.
I would replace either one of Massey and Fonda with Cary Grant In "The Philadelphia Story" and with the clips i've seen from "His Girl Friday" he's also deserving for that performance. Both Laurence Olivier and James Stewart has other performance Oscar worthy too in "Pride and Prejudice" (Maybe some people call it a supporting performance but I'm not) and "The Shop Around the Corner" respective.