I have the 18-135 kits lens, 50mm f/1.8 III, 24-105 mm f/4 L. I actually just purchased the last lens for a great price and I'm loving it when I take it on museum excursions here in StL. I realize I need a wider angle lens and would prefer a zoom so that I could possibly be a walk around lens for me on the trip. I have the slower Sigma 10-20mm that I'm not real crazy about and am considering trading it in for a wider angle, more useful lens.
Considering the Sigma 17-50 f/2.8 or the Canon 17-55 f/2.8. I know the price difference and I realize neither would work on a future FF upgrade. I needa lens that would work for low lit museums/churches and would also work for narrow street photography. I also would like recommendations on what kit I should bring, given my having to lug it around europe for 3.5 weeks. Thank you in advance!