The three are different in many ways.
Robin Williams ~ Amazing actor.
The Dead Poets Society, Bicentenial man, Mrs Doubtfire. An extremely clever man the funniest TV interview I ever saw.
Jim Carrie ~ Impressive best slapstick.
The Mask (superb), Dumber an Dumber (hilarious), Ace Ventura Pet Detective (a joy) Liar, Liar (decent) Truman Show (clever)
Those two made me laugh equally.
Although I enjoyed Eddie Murphy in the Golden Child, the Nutty Professor and the one when he can talk to the animals. Good but not great and not in the same league as Williams.
Jim Carrie made me laugh more, in "Me myself and Irene" was such a scream.