It's hard to choose my top favorites, since I have so many favorites! However, easily at the very tip top of my list are Moses Horwitz, Louis Feinberg, Jerome "Jerry" Horwitz.....better known as Moe Howard, Larry Fine, and Curly Howard....my all time heroes....The Three Stooges! I absolutely love those guys! They were my mentors growing up, and in truth, they still are!!!
As for "serious" actors, Jimmy Stewart makes top spot. He had so many facets to his acting career. He could play humorous roles or serious roles, and could easily fit either style. And he always seemed to be a very personable kind of man! A great talent!!! Next after him, I'd add in Henry Fonda. He always looked natural in the roles that he played....he always seemed very 'comfortable' in his roles.
I'm and old 'black & white' movie kind of guy (especially old westerns), and so I tend to really like the old actors and actresses of yesteryear. I can't really come up with any modern day actors that really stand out to me. Heck, if I could only get the Turner Classic Movies (TCM) and the Encore Western Channel, and RFD-TV, I'd be a happy camper, because if my TV is on, it's more than likely tuned to one of those channels!