Honestly, I can't tell you which breed is the best. When I say that you're probably starting to think Oh great, She can't help me at all But actually that's why this site is here. To help you. So here is my opinion on it.

People use all different breeds of goats for harness. Some may even use does instead of wethers. Though I wouldn't reccomend it due to udder damage that may occur. I have two Toggenburg wethers. They work well but honestly, I don't think there quite big enough. At least clark isn't. The main thing you look for in harness goats is size. Now I know you're probably thinking something like but if it's a kid, how can I tell how big it will get? Well, the thing is, you can't. There is something you can do though and that is look at the parents. If they're fairly large, chances are that the kid will be too. Also if you want a bigger goat don't use a doe. As stated above, they can damage their udders. They also don't get as big as wethers. A wether can pull up to twice it's own weight.

I would also recommend getting a goat that you connect with. Remember, you are going to be working with this goat a lot trust me, I know. If you don't like the way a goat looks, or the way it acts, you will hate working with it and then the goat will hate it too.

There you have it. All in all I really don't think breed really matters. It's just what you like. and what will be able to pull you.