Well, seems like since I got my green belt, my instructors have taken a more keener interest in the execution of actual practical techniques as opposed to subtleties of how to do kata.
One of the things they were talking about was my roundhouse kick. When executing a roundhouse kick, is it better to turn the standing foot on the heel or the ball? My instructor kind of put it a bit too vaguely for me to figure out just from him, so I thought I'd ask all the Muay Thai and Kyokushin people here.
Everything you do should be off the ball of the foot. There should never be weight on your heels.
yep just like KidSpatula said, the ball of the foot. I've known guys who've rotated w/ the heel and done it effectively, that dosen't make it any better though. The only problem is if you lose balance while on your heel you have to move your whole upper body the opposite way to compensate which leaves you way to unerable. If you lose balance while on the ball often the short transfer of wieght back to your heel enables you to steady yourself and regain balance on the ball of your foot. Also, being on the balls of your feet facilitates movement. If you're on your heel, in order to move first you must shift your weight forward then move. From the balls of your feet you can move any time w/o having to shift your weight. Some people say it dosen't matter ball va. heel, but smallest difference in balance and weight-shift can have a huge effect on overall balance and motion.
Definitely balance on the balls of your feet, for all the reasons stated. Being a big guy, turning on the ball of my foot is far easier than turning on my heel.