My first ancient: Constantinopolis Commemorative, Nicomedia, Delta officina. Now I have one from every mint city and nearly every officina. There are a couple officina that I'm not convinced really exist.
An ancient thread, but a worthy topic. I seem to recall similar threads in the last 5 years. I still have my first ancient. A barbarous radiate, purchased some 40 years ago from a tourist stand as a kid, while visiting Trier (Trevorum). My father was stationed in Germany at the time. I remember thinking that this coins must be worth a ton of money because it was sooooo old! Little did I know that I'd end up collecting ancient Roman coins some 40 years later.