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.
It might not necessarily be running. But factorio is a game that's very conducive to you hopping in for a few minutes at a time, so some players have it paused a lot of the time when they're alt tabbed instead of closing it.