I am nikon crop sensor user for past 3 years, then i decided too jump to fullframe 5d markii, i choose canon because i found most "L" lens is cheaper to "N" lens.. I personally did not take the kit, i choose the 24-70mm f2.8L. but if you are the person who like take video, the 24-105mm is great choice. for still image, f2.8 is better..
I think you've got it backwards, f/2.8 is crucial for video, f/4 is just begging for more noise in low-light situations. The 24-105IS is great for stills because the IS allows you to shoot with a slower shutter speed, which allows you to shoot at a lower ISO.
With video, sure the IS may stabilize it a bit, but it does absolutely nothing in terms of allowing you to shoot at a lower ISO.
It's personal preference, I like the 24-105 as a walk around lens for stills, but for video I'd take the 24-70 over it any day.