What guard is best in sparring?

I think whichever the person is most comfortable with is the most effective for them. I use a morph of the two you are discussing. My left fist is about cheek level just below my eye so it doesn't interfere with my eyesight, my right fist is just below chin level. If I have to perform a block with my left hand, my right hand switches to the same position that my left was previously. Now this is if I am right foot back. If I switch stances to left foot back, I reverse the position of the fists.

The only guard that i use is kind of like the taekwondo guard but instead of having the front hand across the midsection i drop it down on my thigh. I prevents any type of thrusting kick, and if you keep the back hand up by your face with the elbow in close to the body then i is very hard to get the torso.

It depends on a number of factors, including the type of opponent you face and what the rules you're using are. Don't get locked into the idea that there's one "best" guard. Whatever guard you use at the moment needs to fill both your offensive and defensive needs. I've seen a few strikers change guards multiple times in a single fight, so get comfortable with the idea of a fluid guard.

With that said, if you're playing full-contact, protect your chin and jaw, as they are along the knockout zone. Generally I have my fists up there but some of my guard positions utilize my shoulders for protection instead.

I use the kickboxing guard you described. With the chin down, hands up to protect the face, elbows tucked in to protect the midsection. I like this guard because its practical for fighting, and its very easy to be mobile. All my techniques can be applied in this stance.

The boxing guard sometimes is the best when you're in mid range (enough for kicks and maybe some punches to hit) but it's really up to you and only you know what works best with you. You'll have to find this by having more sparring combats and see by yourself.

I do taekwondo it is so damn fun