I have both. The difference is sound quality. Neither is bad, just different--and they excel in their respective differences among other comparable models. The MDRs would be considered the most balanced-sounding, no adjustments needed and thus good for all music genres. The XBs are bass-heavy (though adjustable via app), so more ideal for hip-hop/r&b/pop genres.
Their feature differences are self-explanatory. I got both for difference purposes. The MDRs for general use, the XBs for active/gym use.