I like the fact that with my guitar, I can play a range of different styles in a range of different ways. You can differ with the strumming pattern, volume, mute, fingerstyle, range of pick strengths, capo, barre chords/open chords, distortion + other effects, right hand fretting, opening/other tuning, nylon or steel string, hammer-ons, pull-offs and whatever.
I like piano but it the feeling of just pressing down on keys doesn't excite me. Go guitars!