I play guitar (badly) and have tried to play piano and I can honestly say that piano is quite a bit more difficult than the guitar because of having to read both treble cleff and bass cleff and you have to be good with both your hands.
As for learning the instrument; I recommend an instructor. Being self-taught is fine though, hell I'm self-taught, but by being self-taught it's probably easier to form a few bad habits. I still catch myself holding my pic wrong or only down-strumming sometimes. Also, if you go with guitar, get used to using your pinky finger. It'll suck at first, but you get used to it.
As for learning the instrument; I recommend an instructor. Being self-taught is fine though, hell I'm self-taught, but by being self-taught it's probably easier to form a few bad habits. I still catch myself holding my pic wrong or only down-strumming sometimes. Also, if you go with guitar, get used to using your pinky finger. It'll suck at first, but you get used to it.