I am beginning to save up for a wider lens. I've heard good and bad things about both. All of the reviews I've read and all the forums I've been to have said different things about both. Some have told me that the Sigma is crap in terms of build quality and distortion, and to get the Tokina. Some have told me the Tokina is crap compared to the Sigma. I am really confused on which lens is better. The extra 2mm is nice on the Sigma, but I'm not really sure it matters. How much wider is 2mm? The Tokina looks more solidly built and is faster, but then again aperture isn't my main priority. My main concern is IQ (distortion, vignetting, sharpness, color, etc.). So overlooking the obvious advantages and disadvantages of both, which has better IQ?