It depends on what games you're going to be playing, and for how long.The Pro Controller is pretty much essential for Monster Hunter, but I've also used mine for Sonic Racing, Tekken, Wonderful 101, Mario 3D World, Tropical Freeze, Lost World, various eShop/VC titles and currently use it for Mario Kart 8.
It basically provides a much more comfortable alternative to the Wii U GamePad, and has amazing battery life, 80 hours from a single charge. :awesome: