I play piano & guitar as well,
and I love to switch between those two.
With the piano I can compose a lot, it's very easy and versatile for an instrument.
And with the guitar I can express everything I feel to the exact.
Plus, as it's amazingly important, the instrument I use the most often for me is my voice, as it's the hardest to play and you feel so much more related to every note you sing, compared to pressing a key on the piano..
btw: i love that you like shpongle