This is the easiest subject to tackle and since it is always first in the award show it will be first here. I think the Oscars have done a fairly decent job picking the winners in this category. Sure I could think of some that might go a few ways but generally they do OK. I could quibble over Halle Berry winning for Monster's Ball but there weren't any other performances that blew me away that year so why bother. I suppose I could rant about the fact that Maria Falconetti didn't win an award for Carl Dreyer's The Passion of Joan of Arc in 1928 which is widely regarded as the greatest acting performance of all time (male or female)...but the Award was brand new and the film was French so I'll give 'em a break.
The only one I guess seems ridiculous now would be from 1941. Joan Fontaine won for Alfred Hitchcock's Suspicion. Good movie and fine role for Fontaine, but not even close to Barbara Stanwyck in the classic Preston Sturges comedy The Lady Eve.
It seems criminal now that Stanwyck never won an Oscar for acting, although in 1982 she was given an "honorary" Oscar for lifetime achievement. This will become a familiar theme as we examine the dubious omissions of the Academy.
Next we will look at Best Actor which will not be this easy.