Xbox has the bigger library overall, (997 to 783) but most games of that generation don't really appeal to me so my Wii U collection is bigger than my Xbox collection.
I don't think anything on Xbox is quite as great as BOTW, but on the flipside I don't think I played any Wii U game as much as I played Star Wars Battlefront on the Xbox.
Seems like this was a good matchup, the poll results so far are incredibly close.