Hmm. If I bought an ultra wide right now, I would likely get the 11-16. Though I am tempted by the Sigma 18-35 f/1.8 which could fill two roles. It's not an ultra-wide, but from what everyone is saying I don't really need one. I think I just need to do some more shooting with my 17-50 and see if I really want to go wider. Perhaps borrow my dad's 12-24 a few times.