A few years ago this was easy. After The Departed and The Fighter I might have to go with Walberg. Plus Walberg is a producer for Entourage, Boardwalk Empire and How To Make It In America I believe.
I can't really think of a single Will Smith movie that I like. Honestly his movies are so stupid, and it's sad because I think he is talented.
Mark Wahlberg was in The Departed which is my 2nd favorite movie of all time. He wins on that alone. Fighter was so awesome, too. Marky Mark has a pretty damn good resume.
Wahlberg isn't the mega star that Smith is, but he is just as good of an actor. They've both made really good movies. It's hard to say who is better. I like them both and don't have a preference. Each has a different set of traits that allow them to be perfect in SOME roles and good in others.
I used to love Will Smith but other than Independence Day and Bad Boys/2, his movies haven't been that great.
Without a doubt, Mary Mark. He's a good actor even when it's cheesy roles like Rock Star.