There are far more self-taught guitar-players than pianists; they may not be very good, but they can make an acceptable sound, whereas self-taught pianists are likely to sound pretty awful. So there's your answer!
Guitar
A half guitar half keyboard is called a Keytar
Piano and Keyboard
Guitar and Bass Guitar, sometimes slide guitar, drums, keyboard/piano, even percussive instruments
guitar, vocals, synthenizer, keyboard, violin,
A bass guitar is easier than playing a guitar or drum set or keyboard while singing. But singer/keyboard player is a very common combination.
I think a keyboard is easier to learn and more logical than learning guitar chords. Guitars have a certain coolness and of course many teen idols play guitar like Sweet Baby James.
Guitar
Guitar
keyboard guitarman, mr.! keyboard guitarman
A half guitar half keyboard is called a Keytar
Piano and Keyboard
guitar is cooler, and so is keyboard
Guitar and Bass Guitar, sometimes slide guitar, drums, keyboard/piano, even percussive instruments
Piano's, Keyboard's, & a Guitar
guitar, vocals, synthenizer, keyboard, violin,
its easier to play on guitar, but its far easier to master on the controller (which is better for the long run)