What sells best? Shorts/Novellas/Anthologies/Novels?

I'm wondering, for those who are published or have inside info, what length book sells the best? And does it vary from e-pub to e-pub?

I heard an EC person say that novellas seem to sell very well. I'm also wondering, what pays the best? Based on what EC charges for quickies vs. novellas vs. novels, it seems like quickies would pay the best, on a word-count basis. But if quickies don't sell that well, and the longer books do, then I guess the longer books would pay better in the long run.

Any thoughts?

I know everyone says "write what you like". But if I don't have a preference for a particular length of book, then I'd rather write what pays.

Congratulations!

I just got my nook, and I'm loving it. I've always liked longer books (assuming the story is good), but I might be leaning towards the shorter books now. Seems like with erotica, I really need a good, complex story to keep me interested for a full novel.