I started originally with a serie of our cents, found in circulation, when I was a young kid. When I had them all, I switched to the next denomination, the stuiver (5 cent) and then 10 cents. Later, when I had more money to spend, it became the other denominations as well, one of each year and when available, all varieties.
At some point I decided to collect "one of each" form the countries I (had) visited. This ended up in my type sets, where I want "one of each" where different compositions, different mint marks, different designs and varieties all count as a different type. But this only for foreign coins.