I really do like both of these covers, but I think the US one is pretty spectacular (it's also the edition I own). It just screams EPIC FANTASY, which is what I think these books deserve. I mean, they're huge and clearly well-loved on an epic scale, so... why not represent that with the cover? Everything about Tor's US cover draws me in, from the string colours to the title font. It's all ace.
The UK Gollancz cover is nice too, though more understated, I think. I actually do prefer the title and author name placement, as it's less confusing at a first glance. The main image doesn't really do anything for me, but I like that it's in keeping with the rest of Brandon Sanderson's UK cover designs.
Do you have a favourite?