photozone has sample shots taken of a grid so you can check distortion (hover over the different focal lengths to bring up the other test shots). No 24 1.4 review up yet, unfortunately.
http://www.photozone.de/nikon_ff

The 24-70 distorts significantly, IMO, at 24mm.

The 14-24 not as much at 24mm.

Your best best is USUALLY a prime, that is intended to only be, obviously, at this focal length and usually the engineers have corrected for this. I have not, however, tested the 24 1.4. When I owned a 24 2.8, it wasn't that bad.

the 24 1.4 would probably be your best bet. But at $2200, it's $400 MORE than the 14-24 or 24-70 2.8, and obviously "less useful", so. . . .

that article is pretty cool. I am getting an iphone app to help with the DOF piece. Now if there is only a comparison of the barrel distortion and pin cushion effect between the lenses. For group photography, i dont want the people on the edges to look stretched out.

I "only" have the 14-24. It exhibits noticeable (but easily correctable) barrel distortion at 14mm. At 20mm, it is neutral as far as I can determine. At 24mm, it is ever so slightly "pin-cushy", but so faint that I practically never correct for it.

While distortion (or the lack thereof) is a function of the optical skills of the designer, DOF is strictly geometrical, i.e. any 24mm at f/1.4 will exhibit exactly the same DOF.

Here is a link to a DOF calculator http://www.cambridgeincolour.com/tutorials/depth-of-field.htm . You may find that useful.

Barrel distortion can be different on various lenses.

I do a lot of people photography (in groups, stage, etc), and i wanted to know, is 24mm equal in all three lenses Nikon 14-24mm f/2.8, 24mm f/1.4, 24-70mm) in terms of barrel distortion. I know that focusing and bokeh could be different, i.e. 24mm f/1.4 produced different depth of field than a 85mm 1.4 (or is that wrong)?