best walk around

I second the 17-50 non-VC. Great lens for the price. I 'upgraded' to the VC version for about a month, but always felt the IQ was inferior to my old VC.

Tamron 17-50 non-VC or Sigma 17-50 OS. Can't go wrong with either. Optically they are very close, Sigma has slightly faster focusing and OS.

24-105 F/4L is a real great lense also for walk around

mcowens wrote in post #13813359
24-105 F/4L is a real great lens also for walk around

OP specified they were looking for an f2.8 lens...

However, OP didn't say what lenses they already have and, well, sometimes in low light f2.8 isn't fast enough either... So a slower walk-around lens complemented with some faster primes (Canon 28/1.8, 50/1.4, 85/1.8 or Sigma 30/1.4, 50/1.4, 85/1.4) might be a better approach.

Some "problems" with f2.8 zooms is that they tend to be pricey, and/or you lose a lot of focal length range, and/or many of them are fairly large & heavy.

Canon 15-85. About as sharp as most of these other recommendations and a much better range. Downside is variable aperture, but it doesn't matter much in the daytime, and you should be using a flash or tripod at night anyway.