A lot of reviewers say rounded aperture blades on a lens will give good bokeh. That's largely false, a rounded aperture opening will produce round blur circles rather than polygonal (which is preferable), but it has no effect on how smoothly those blur circles blend together. The latter quality is really much more important. So discount any reviews which base their assessment purely on the shape of the aperture.
Most reviews which explore bokeh further usually do so only at close range, where the background blur circles are largest, and usually looks smoothest. That is only of limited use since most pictures are taken at medium-far distances. At far distance the DOF of a wide lens may extend to infinity so bokeh is not relevant (except in the foreground). At medium distances the DOF can still be surprisingly small, especially when the image is viewed large, so bokeh is still a very important part of the picture. In my experience this is the region where many lenses struggle.
This is why comments on bokeh vary so much.
For what it's worth, the Sigma 35/1.4 is known for being very sharp, but the bokeh is rather harsh. In contrast the Nikon AFS 35/1.4 is not as sharp but produces a more pleasing "rounded" image. I suspect the same is true of the Sigma 24/1.4 vs the Nikon 24mm. But note I have no direct experience with any...
Is it possible to go to a shop and try the lenses you are interested in? Ultimately you are the best judge of which lens performs to your liking.
