I wouldn't say that it's the best, but it definitely is a good one. I don't know many people outside of my gym who do this, but the lead leg round kick can be a great setup for punches. By stepping down on to the kicking leg after landing the strike, you can put more 'oomph' into a punch than you'd think.
A popular combo in my gym is the inside leg kick into a jab, cross, then darting into an outside leg kick. By throwing out the jab before your foot even lands, there's virtually no break in the combination.
A lead leg round kick to the body can be used similarly, but you'll step down too close for a rear leg kick. I'd just commit heavily to a jab-cross-hook as I'm stepping down.
Another one that I like is a lead high kick (no switch) followed by a cross, lead body hook, then a darting rear leg kick. When your opponent blocks the high kick, it'll freeze him for a second, leaving you enough time to step down into the cross. The cross may or may not land, but it will definitely lift his guard high, leaving an opening for your body hook. That body hook will load up your hips for the darting/springing kick, which will tidily wrap up the combo by taking you off angle.
What I dislike about leading with a kick is that my leg is so open to be countered if I miss. And coming from a San Da gym, it's easy to get caught and thrown if my kick doesn't come behind something.
Highly opinionated but out of touch with the current MMA scene.
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