Including DLC, micro transaction purchases, etc. If you got a game for free, please also list your non-infinite next best.
For me it’s Team Fortress 2. $100 total spent on hats and the Orange Box back in the day, 4200 hours plus of fun, meaning 2.3¢ AUD per hour. Initially I thought DotA2 would be my best but it turns out I’ve spent a lot more money in that game than I thought…
My worst is God of War: Ragnarok. Bought it full price for $95 AUD, only played 2 hours and hated it, meaning $47.50 AUD per hour.
Per monetary value, Animal Crossing.
Regarding free games, a played a lot of Dwarf Fortress back when it was free and still ASCII, and of course LPMUD, which I played for thousands of hours back then. I even wrote a front end/client for it.