Following is a bokeh comparison between five 24-something lenses with a few additional L prime lenses thrown in the mix.
All lenses and focal lengths were tested using a stationary (tripod-mounted) Canon EOS 5D Mark III. The same focus target was used for all test shots and manual focus was used to obtain ideal focus for each focal length tested. Focal length marks on the lenses were used for establishing the focal length setting for each shot.
The relatively wide angle focal lengths found in these lenses need a close subject and relatively distant background to create a strong background blur. Perhaps the biggest difference you are going to see below is that the 24-70 L I acts as a longer focal length lens than most of the other lenses compared here at this relatively close focus distance.
See the appropriate review for the full discussion of these comparisons.