It depends on the Kingon and depends on the Wookie. In single combat, I'd have to say the Wookie, they are much bigger, and much stronger. But as a whole, I would say the Klingons would conquer the Wookies. An individual Roman soldier might lose out of a barbarian, but the legion may well be stronger than the barbarian forces.
Now, the Romulans wouldn't to anything as crude as direct combat. They would use some scheme that had a high potential for gain, low percentage of success and low cost. If it doesn't work, just abandon the mission, and try something else later.