Guitar... it's such a melodic, yet rhythm-based, technical instrument, and I already play drums of course. What the guitar is playing often determines the drum groove, so it would be cool to have some control over the melody, progression, and overall musicality of my ideas.
I play guitar and bass guitar, though I don't know how to read music and don't know theory. I wish I knew it, but I also write songs and wish I was better at recording and making he song sound good. I write decent songs, but don't have a good voice either, I still using it or whatever er I require for the song, but it's not always great