Most Helpful Girl
I play the piano, ukulele & violin. I took many years of piano & I had no lessons for the ukulele or violin. I almost want to say in the long run, piano is harder because you can do so much. Violin was hard to pick up but once I got the hang of it, it was a breeze for me from there. Ukulele was easiest, by far. I tried the guitar but I was small hands & I find it hard to do chords on my acoustic, so I gave up.
Most Helpful Guy
There is no right answer for this. They're all difficult at a high level. I'd say piano is unique in that it's self-accompanying and requires a greater level of coordination, especially for playing over complicated left-hand rhythms.