The thing about piano is that if you learn to play, you generally learn a lot about music and theory and things that someone just picking up a guitar wouldn't learn right away. Notes are arranged in a much simpler way on the piano so I find certain things can be done easier on the piano and then transferred to a guitar perhaps. Pianos are very versatile, and a very useful instrument for a musician, this might be what she is talking about by saying it's the best instrument. I think that this song is just meant to be very ironic though, because no matter how great, influential and useful pianos can be...there is no piano in the song.
The thing about piano is that if you learn to play, you generally learn a lot about music and theory and things that someone just picking up a guitar wouldn't learn right away. Notes are arranged in a much simpler way on the piano so I find certain things can be done easier on the piano and then transferred to a guitar perhaps. Pianos are very versatile, and a very useful instrument for a musician, this might be what she is talking about by saying it's the best instrument. I think that this song is just meant to be very ironic though, because no matter how great, influential and useful pianos can be...there is no piano in the song.