Nuendo has unique features which are mainly useful for sound-to-picture and(increasingly) game audio work. For everyday music production there is little-to-nothing to choose between them, Cubase is usually half a development cycle AHEAD of Nuendo.
I slightly prefer the Nuendo look, I hate some of the new features which have appeared in Cubase (and now both platforms) over the past few years, the mixer is CARP. I have licenses for both but haven’t updated Nuendo for a while, may do so with the current promotion with an eye to the future but frankly don’t like what I’m hearing about N8. But then the latest Cubase has issues too…
Still wouldn’t go back to analogue tape though…