This was a battle that really depended on what kind of technology King K Rool had obtained in the past. I think King Ghidorah would win this fight if it was man to man, but King K Rool has been known to show up with cannons and hovercrafts. He should be able to outspeed King Ghidorah and dodge any attacks that are headed in his direction. He can then counter with his cannon until the King finally falls. King K Rool wins.