For landscapes ,if you go for the 17-40 f4 L, the IQ is excellent in daylight and on a crop body it also will make a very good general purpose walk around. On a FF, It will absolutly be wide enough, just watchout to keep your toes out of the shot! I have both a 30D and a 5D and use it on both. The 17-40 will cost a lot less, and unless you are going to shoot in low light, f4 willbe fine. For landscape you will probably stop to f8 or f11 anyway.