For me, I find the 24-XX zooms to be near perfect.
Since I only used digicam before, and with max 35mm at the wide end,
I don't find that 24mm on a crop camera is really limiting for my need.
If I walk around, I will use my 24-85, or maybe a new 24-105, still deciding.
But if I want to go wide, I stick with my 12-24.
With good planning of what I will shoot, I find that I bring only one lens and
never seem to need another focal. So I'm pretty happy with the market offering
of 10 to 24mm for wide, 24-70 for normal and 70-200 for long.
The only thing is your personnal preference. And only you can answer that question.
If you already have a 28-70, plan on going real wide, like the EF-S 10-22.
The 17-40 or 16-35 are superb lens, on 1.3x or FF since they provide 16-17mm wide.
To replicate that on a 1.6x, you need 10-12mm.
Hope it helps. I know it's confusing choosing a lens. I'm in the market for one 