Anonymous wrote:I think there's a difference between what is hardest to get started on, and what is hardest to master.
Piano is relatively easy to start on. Even a beginner with one year of lessons can play something that sounds decent, albeit simple. But playing it at the highest level is incredibly hard.
On the other hand, a fretless string instrument, especially played with a bow, is hard to start, and sound bad for a long time. But playing violin at the highest level isn't harder than playing piano at the highest level.
Piano player here and I agree. Assuming your piano is properly tuned, you never have to worry about intonation, which is a huge part of playing almost every other instrument. You touch a key in any manner, and it will always play the right key, always in tune.
Mastering it is another story.
I also think the instruments that require breath and embouchure are really hard.