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.
Neverwinter Nights, hands down. I played it 20 years ago and until recently I was DMing a weekly campaign using it, but I would guess I’ve put between 20,000 and 25,000 hours into it over the last 26 years. Honorable mentions for Baldur’s Gate 3, Elden Ring, and Indiana Jones and the Great Circle, which I’m currently playing. (Spent all day today playing it, in fact.)
Least enjoyment? I pre-purchased Batman: Arkham Knight and quit it after one hour, so that’s an obvious choice.