It really depends on the season/my cravings, but my all-time favorite will always be coconut Italian ice.
Mini backstory: When I was about five or six years old, my mom/dad used to take me around Ironbound (Newark, NJ) during the summer where they would have these little icecream carts on literally every corner. It would cost a dollar for a full cup of icecream, and I would always beg my parents for one any time we were near them. I don't remember having any other flavor besides coconut, but what I do know is that coconut is my dad's favorite too, so maybe that's how I got hooked on it.
I could go for some vanilla bean icecream right now, though.