Pianos have a really nice clean sound to them and can play fast consecutive notes with ease. It's also easier to learn because everything just goes up, and it's as simple as pressing a button.
Guitars have a really cool unique sound to them, however I find it more difficult to play. The strings are taking me some getting used to to make sure I don't screw up the note with that weird vibration sound against the fret bar things. It's also pretty portable.
Keyboards can select any instrument including guitar, is still easy to play, is still easy as pressing a button and is more portable.
Keyboard wins.
Poll