Great prints have been made with both systems.

IMO, some of the arguments in Jensen article piece (link provided above by Doug) are nonsense. Comparing shadows cast with sunlight to shadows cast by diffused fluorescent light completly ignores the enlarging lens. After arguments have been made to persuade many readers that sunlight and shadows shows the collimated light sources are superior, the enlarging lens is finally mentioned and conceded to have some role in the process. There is also use of moralistic words rather than technical terminology, e.g., diffusion density isn't "washout", nor is it "flare".

For a truly excellent and scientific comparison of diffusion and condenser sources, try to find a copy of "Controls in Black-and-White Photography (2nd ed)" by Richard J. Henry. It is out of print but can be found at the internet used book search sites.

If you want to compare sharpness from the two types of enlargers, be sure to carefully match the contrast of the prints. A more contrasty print will be perceived as sharper.