Mine was actually piano for 2 years, and then I played saxophone for 14 years. I picked up a guitar very late - I started guitar at 16 and then it was all over. I played guitar for the rest of my life. I love studying it, learning it, and expressing myself with guitar. It's really my tool for communication. Saxophone was beautiful, but I didn't bond with the instrument as well as guitar.
I'm still grateful for the piano and sax skills. They help!
What was your first instrument?