I found DDX to be pretty similar to Xtol in regard to sharpness and shadow detail. It does work out more expensive per roll though (if that's a concern to you), but—as it's a liquid—more convenient if you're not using it frequently.
DD-X and Xtol are quite different tonality wise, so they compliment each other nicely in high and low contrast illumination. You can overcome the higher highlight contrast by slowing agitation (using DD-X) but it does have a bit more intense highlights than Xtol. Both are truly excellent products.
"Often moments come looking for us". - Robert Frank
"Make good art!" - Neil Gaiman
"...the heart and mind are the true lens of the camera". - Yousuf Karsh