The very best standard zoom for APS-C cameras is the 17-55 f/2.8 IS. It covers wide to moderate telephoto, so it's useful for most types of portraiture. If you don't need the f/2.8, the 15-85 f/3.5-5.6 IS is just as good (if not better), and covers the most-used wide FLs (15-22mm) and the most used portrait FLs (50-85mm).
The 24-70, on APS-C, is a short telephoto zoom, which is a less useful general-purpose range.
Landscapes are done with all focal lengths, not just wides.
whitehawk wrote in post #9791604
The 24-70 is an EF lens which means your focal length will be ~38mm-112. I'm going to second what Ipj8 said - If you want to be able to do landscapes you will appreciate the wider angle of the 17-55.
Focal length does not change, and it's pointless spouting 35mm equivalents when the vast majority of current photographers aren't familiar with 35mm in the first place.