I would agree with the Dreamcast having the most consistently good library, for sure.
Look, I like the Wii U, but I strongly disagree about it having a consistent library. Once you get past the 25 or so good games from Nintendo, the quality completely drops off like a cliff into nothing but shovelware, movie tie ins, and rereleased PS3/Xbox 360 games. There are barely any exclusive worthwhile third party games on the console either.