Started with phpBB2, then moved to some random forum software that wasn't popular (don't even remember the name), then phpBB3, then finally settled into IP.Board. (Don't ever plan to change from IPB)
Well I started out on Proboards then from there I went to SMFforfree then back to proboards sadly. However I did go to invisionfree and free forum (phpBB) once but wasn't successful and I didn't like how it looked.
I started with vBulletin, As someone had a site and I wanted to learn to code for vBulletin. So I just look into the coding day in and day out. And still have a vBulletin license to this day