I think guitar. My favorite is when he's play electric guitar without a pick like an acoustic, during the Live 2012 version of Mylo Xyloto (The dvd/ Live album) and the 2009 viva la vida tour one, from Tokyo, streamed from MTV. (You know, the one where they transition into talk out of no where. And it's a gift from the gods). He just seems to enjoy guitar, instead of slamming on the piano. Don't get me wrong, I love his style on both, but, guitar all the way :)