I know they're both important, and I would dearly love to open this up to a larger forum and hear what others think on this subject. Or perhaps someone with a larger audience might like to take up the question on their own blog?
ETA: Yes, this is mostly a rhetorical question for the purposes of discussion. As I said, both are important.
In my current state of mood, and having read far too many writing blogs for my own good, I'm thinking that voice ultimately trumps worldbuilding.
If book A has breathtaking ideas but writer A can't write h/er way out of a paper shroud, will a tree fall in the forest and still make a sound?
No wait, I said that wrong. How about this: if the worldbuilding is chock full of amazing ideas but the execution is poor, it seems to me the book will probably not sell or find an agent.
But I could be wrong. It has happened before. I'm sure you could come up with a few names as exemplars of good ideas/bad writing who have managed to get published and flourish, but I have to think they are exceptions. Or are they?
Perhaps this is a better example: If writer B, for instance, has good worldbuilding, and is a solid writer, but doesn't have that spark of voice, that fresh way of telling the story, I'm not sure they can break through. Whereas writer C may have so-so worldbuilding, but a fresh and original voice, and gets a 3-book deal.
Or can they? Which is more important--voice or worldbuilding?
