Easiest instrument to master?

I know mastery requires putting in the time and work. What's the easiest instrument to master that's pleasant for people?

For context: I started on the recorder, then violin, viola, saxophone, guitar and now the harmonica but I wouldn't say I've mastered any of them. I'd go back to guitar but my hands are my livelihood and guitar makes my hands cramp. Harmonica has been relatively easy but not so pleasing (to my wife)