I think the distortion argument comes down to what you're shooting. For interior/architectural work, the less distortion the better. However, for landscapes and candid stuff you probably won't notice the distortion.
Now, I know ken rockwell isn't all that popular around here, but bear with me. In his
ultra-wide shootout, he talks about the distortion of these lenses (most here would agree, the tokina is optically the same as the pentax). If you look at his guide image, only when you're deliberately trying to show the distortion in a landscape shot does it become visible. If you ignore the top inch of that picture, you'd be hard pressed to point out any distortion. It doesn't really matter in the landscape realm.