You guys really could be a little nicer to each other... and that counts for what ever opinion you have...
I go with Gaara, it'd be hard though.
Sasukes 2 elements just do not really work. Neither amaterasu. So he has to go with susanoo. But susanoo actually is more a defence then an offence. Well, those arrows, I'd say we just don't know if they would get through Gaaras sand, I'd say yes, but they won't hit, because it can't be hard to make them miss with that much sand (a little like Neji vs that Spiderguy).
But Kirin surly would get through that Sand and blow Gaara away, but I just don't see Gaara waiting that long. I think Gaara could end it before. And besides, if Sasuke has to go with susanoo, it'b be hard to prepare for kirin.
And to that glas thing, heat allone actually can melt sand and if it cools off again it is glas-like. This would shadder easely and Gaara could use it as he pleases. And no, I don't think, that Sasuke could melt all the sand.
Kakashi:
If it was Gaara vs Kakashi, i go with Kakashi, he just has to many jutsus, and on top of that, Gaara really does have a wather weakness. Kamui would hit Gaara aswell, Gaara is no runner, he just blocks, and that doesn't work against Kamui. And even if tha sand was faster, it doesn't help, all sand gaara sends in against kamui just gets warped away. (Besides, that's why that arrow was warped away so fast, it flu directly into it.)
And to also consider that: Sasuke vs Kakashi
Here I'd go with Sasuke.
And do not argue with, Sasuke wins over Kakashi, Kakashi wins over Gaara --> Sasuke wins over Gaara. It's not that simple. (it's kinda like Rock, Paper, Scissors)