Worf stood up pretty well to Jem Hadar in hand to hand combat, when he was held prisoner during a portion of the Dominion War (on Deep Space 9, for those who don't know). Considering that the Jem Hadar were genetically engineered specifically for combat, this says a lot. Wookies are great warriors and their size and strength would give them a slight advantage over Klingons. However, Worf has proved time and again of his prowess in combat against a variety of foes, often much stronger than him. Wookies have a weakness of being slower and more cumbersome, especially when compared to Klingons. Chewbacca, also, has never been shown as having too much proficiency in actual hand to hand combat (in any of the SW movies). I think it would be a great fight to witness. Both would put up a great challenge. However, in the end, I think Worf would ultimately come out on top.