Android N finally might bring the TouchWiz features that have made it so usable. But all things equal, I think I'll still take Samsung's hardware over any other OEM Google picks.
I think superior screen, camera experience (notice not just the camera but the actual experience because TouchWiz's camera app and features are superior), waterproofing, wireless charging (will they bring it back for nexus devices?), and other little things like superior design and compact sizes makes me lean toward Samsung.
But who knows. On the nexus side you get a more bloat free experience and faster updates/support. I may yet be swayed. It's up to Google and the OEM they pick to come through with a challenger to Samsung's hardware.
Either way, it's about time Google adopted more stuff from TouchWiz, the software we love to hate on but forget we owe to it many useful features.