There is no such thing as "best"... so the answers will be varied greatly. This is the reason people (like me) have purchased, resold, purchased, resold and purchased numerous of lenses in search for a lens that fits.
For me, the zoom 24-70L is not a good walk around lens. The focal range is short and the lens is a bit heavy. For others, (especially those that like the f/2.8 max aperture) it might be ideal. Yet others, (like me) traded in the 24-70L for a 24-105L which is a compromise of the f/2.8 for other advantages. Yet others, are going to find the 24mm focal length not wide enough. This is especially true on cropped sensor bodies. They choose the 17-55 f/2.8 EFS lens. Yet others, do not find enough advantages in the "L" line of lenses and are perfectly happy with the 28-135 IS. My cousin is one of those individuals.
Finally, many shooters (including Iron and I) actually prefer primes of zooms but the OP did specifically say zoom. If you are tired of switching between two zooms, then I don't think primes are a good fit.
I also have fairly older zoom, the Tamron 35-105 f/2.8 Asph. Its old and slow but I keep it because it is also good image quality for a second body.