Now this was told to me by a guy who trained in Thailand. He was at one stage the Muay Thai champ of New Zealand. His name is Terry Hill, if you check his background, he is all that and a bit more.
First he told me the stories of the great Kung Fu masters that went to Thailand and got their asses handed to them by the Muay Thai guys.
Then he told me of the great Karate masters thet went to Thailand and got their asses handed to them by the Muay Thai guys.
Then he told me of great Judo players that went to Thailand and handed a bunch of Muay Thai guys their asses.
Now you have to remember that all these fights were fought under Muay Thai rules. These Judo guys are the reason that ground fighting is not allowed in competition these days.
Q: You want to know who would win?
A: The side that changes the rules to suit themselves.
If you mean without rules, then it would depend entirely on the practitioner.
I hope this answered your question
--Dave