There is a consideration in all fights.
"A well trained big man is better than a well trained small man."
That being said, I do not consider it a real competition on any level. But anyone can be beaten in a given moment under the right circumstances. I would go 2 - 1 in favor of Dolph.
@ John, Tony Jaa is a highly trained Muay Thai fighter in the "Old School" tradition of Muay Tai fighting. Dolph Lundgren may be an actor but here is some of his personal Bio information:
It was in the military when Dolph first came in contact with the martial arts. Five years later, Dolph had become a World-Class competitor in Japanese Karate and was deeply involved with a discipline that was to become an important part of his life. He has been awarded his Third Degree Black Belt by the World Karate Organization in Tokyo. His accomplishments include being the Captain of the Swedish National Karate Team, as well as a Champion of the Swedish, European and Australian Heavyweight Division titles. Lundgren still regularly performs Karate exhibitions at international tournaments worldwide. In addition to his Karate expertise, Dolph was selected by the U.S. Olympic Committee to serve as the Team Leader of the 1996 U.S. Olympic Pentathlon Team during the Atlanta Games. He is actively involved in promoting the image of this sport.
So I guess,... yeah, you could say he's "Just an actor."... but you'd be wrong.
Dolph Lundgren bio on IMDB.com