EFS17-55_F2.8 IS or 17-40_F4.0 L ?

I owned 20D, I need lens for traveling , landscaping and Area Photography , often with strong back lightning, eg, Sunset or white clouds back grounds. Cheap lens tends to flares and soft.

F/2.8 and IS is great but the price is high and its EFS.! While the 17-40 F/4 is is L quality and less expensive. I am confused, which one to get?
what do you reckon? Thanks for your comments.
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a picture worth more than a thousand words... keep on shooting.... josan
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