Ubuntu was my first. I got a copy of 7.04 from the IT instructor at a local tech school during a field trip back in high school. I had no idea what linux was before then. I would boot the live cd on the family computer and mess around with it since I didn't have one of my own. I was finally able to get a hand-me-down windows 98 PC from my aunt and installed my copy of 7.04 on that right away. Got my dad to run some ethernet up to my room and I was living like royalty after that.
I've tried about every distro under the sun since those days, but Ubuntu always feels like home