An even better alternative for the Canon EF 17-40mm (yet more expensive) is the Canon EF 16-35mm f/4.0L IS USM. While they cover pretty much the same field of view, the 16-35 mm is an overall sharper lens, with less cromatic aberration and geometric deformations on the edges. You will pay some more for it but if quality is paramount for you, it will be worth it. The even better alterative is the Canon EF 16-35mm f/2.8L III USM – with wider aperture for better results in lower light and even better image quality. Of course the price will be higher, but as far as gear is concerned, my advice is to buy the best you can afford, right from the start.
Canon EF 16-35mm f/4.0L IS USM Ultra Wide Angle Zoom Lens