[flake]

I don't think it's reasonable to suggest that you should only consider the 12 -24mm if you are planning to upgrade to FF Chris, on crop frame it certainly outperforms the 10 - 20mm in terms of distortion, it vignettes less (probably being a FF lens), resolution was about the same, although the 10 - 20mm beats it on CA's.

Most of the lenses in this sector perform to a very similar standard, personaly I don't think that because a lens is FF you should discount it. Aps C isn't dead but FF lenses do usually perform better than dedicated Aps C ones because they can take advantage of the sweet spot. The fall off in resolution of the 10 - 20mm towards the edges of the frame is marked, you can see it in your images, it's much less so on the 12 - 24mm. This is not recoverable in Post processing, once it's lost it's lost.