I'm in the market for a wide angle lens. I've been reading review after review and I can't make my choice. I've narrowed it down to 2: Sigma 10-20mm or the Tokina 12-24mm. I'm looking for something I can use all the time. From the reviews, it seems that the Tokina is a sharper more all around lens, but the Sigma is more fun and can go wider. Which would you choose and why? P.S. I think I can get a used Tokina for $350 shipped, but I'd have to buy a new Sigma.