I wouldn't pick Party U. If you get it retail, you get a controller with it free.
I would pick Pikmin 3. I didn't think it would be my type of game either, and seemed sorta niche. I bought it on a whim and very surprised by it. Great game.
BUT, since I already owned all the other choices when I bought MK8, I had no choice but to choose Party U (was planning on getting it anyway)