Please help. I have an opportunity to purchase either a canon EF 17-40 F/4L or Tokina 12-24mm f/4 which are both in great shape for used lenses. I have a canon 20d and need to take an occasional wide shot when I go to the mountains. I have the cash for either so which do you recommend?? I know the canon has a better build and reputation is great and I can get it for about $565 wheras the Tokina will run me about $300. Please help me make up my mind before I lose the opportunity. I usually seem to be taking most pictures around the 75mm focal length with my 20d but seems the wide angle would be better for mountain shots.

