Hi Marc and Austin,
Being a very happy Canon EOS 1vHS user, I thought I might throw a grenade into your discussion.
These days I use my Canon EOS outfit for no more than 20% of my shooting - the stuff that demands super fast responsiveness from the camera; AF that is reliably very fast; auto-flash for things like parties etc when you have no time to mess about with flash settings and available light is just not on! Blah blah.... the list goes on - an obvious horse for a specific course.
I use Leica M7 and lenses for when 35mm is the right horse for the course but auto-everything Japanese machine guns is not called for.
Otherwise, I prefer to shoot Hassy 6x6.
I mention this because I have both the EF 70-200mm f2.8L and EF 24-70mm 2.8L.
IMHO, the 70-200 is an OUTSTANDING lens and enjoys a well earned reputation as just that - at each "main" focal length like 70mm, 100mm 135mm the image quality is worthy of any subject and consistent from axis to the edges. Some testers have said it is as good as prime lenses! (a big call I know). All aberrations are so well controlled. I love the images this lens makes especially wide open. It seems that Canon has a special skill with medium tele to long tele lenses.
But, alas the 24-70 involves "trade-offs" (stands to reason when going from very wide angle to short tele). I have never ever used a super-wide (wider than 28mm if not even wider than 35mm) Japanese lens that made me happy like I have German wide angle optics - I think it is fair to say that the Germans have dominated wide angle optics.
BUT, I really enjoy using my 24-70mm and its images. Its range is so useful for "machine-gun" style shooting. The optical aberrations are reasonably well controlled / balanced - the trade-offs have never alarmed me (but I am just an amateur shooter...). Yes the 24-70 does suffer from distortion especially from about 35mm to its maximum 24mm - I have to be very very careful how I hold the camera to avoid worsening the distortion. Definition in the field to edges is relatively low when used wide open.
Now, I should say that this distortion is IMHO not really blindingly bad nor is it anywhere near as bad as most Japanese consumer zoom lenses. I also think it might be a fair way behind Canon's prime lenses of the same focal length - stands to reason.
BUT as a tool it does do the job well so long as I keep in mind it's distortion limitations when shooting wide - taking great care with camera angle.
I replaced my EF 28-70 f2.8L with this lens and I still think it was worth doing for the extra angle of view and also because I think its overall performance is better - but I will understand if there are others who disagree.
But, as my machine-gun workhorse the 24-70 does the job.
And, if I am taking more serious images where optical quality is very important, then I'd never use a zoom (except the EF 70-200 f2.8L) anyway.
Then again I'd always chose to take my M7 and Leica glass!
Come to think about it, I'd be more inclined to take my 501CM/503CW kit with Zeiss glass - system of first choice!