The 17-40mm is definitely a popular lens. In terms of which has the "best" IQ, I don't know. Of the three, the 24mm f/2.8 has a slightly better MTF chart (on Canon's site), but MTF doesn't equate to image quality, since there are many other things like color saturation, CA, vignetting, distortion, and bokeh that all affect the way an image is perceived.
If you want the wide angle for landscape, I think you'll find a lot of people voting for the 17-40. If it's more for street photography, you'd probably want a faster prime. There are also some interesting specialty options, for example if you don't care about autofocus or filters, there's a Samyang 14mm f/2.8 that is about 1/5 the price of Canon's.
Anyway, as always, the choice is up to you, but I hope this helps.
