Vaati is a better choice for many reasons, being the second most-recurring antagonist throughout the Zelda series, as well as being said recurring antagonist in the Toon games. Just as all four Mario newcomers being revealed so quickly is suspicious as to whether there is a Mario newcomer on the horizon, the fact that Toon Link was not only revealed so early on but before Zelda is suspicious as well (Wind Waker HD promotion aside) and kinda makes you wonder. Now, that being said, Wind Waker and Spirit Tracks are no Four Swords Adventures, and Vaati has no involvement in them, so that doesn't necessarily mean anything, but he is popular and relevant to the series, moreso than the one-shot Ghirahim - who, if you wanna go all conspiracy theory considering the end of Skyward Sword, could be reincarnated into Vaati, considering their similar appearance - and he is depicted as having great magical abilities, something that the roster currently lacks big time (the only true magic-based fighter being Zelda).