NSMBU is legitimately good btw, really good level designs for the most part if you can stomach the NSMB aesthetic. New Super Luigi U is included too which was originally DLC, all the levels are less than a minute but they're surprisingly fun too.
Mario Maker is letting players make full-on 8 world, 40 course "games" and share them with friends. It also comes with a lot of built-in levels by Nintendo. Haven't played them though so can't vouch.
Not sure you could really go wrong with either tbh, but with both being the same price, I will say Mario Maker is a lot more relevant at the moment and the concept of sharing levels with friends is inherently awesome.