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.
Excluding free/infinite, I’d have to say my best is Morrowind, probably, but it could also be Sim City (Classic or 2000), Starcraft, Half-Life/TFC, Team Fortress 2, Super Mario World, or Mario Kart.
Worst is even trickier, as I’m very careful about my game purchases (excluding Humble Bundles that are technically infinitely bad because hours played is zero, but don’t count because I paid to get some other game and/or donate to charity). It’d probably have to be some old early '90s game my parents bought for me, not anything I’ve bought for myself. I remember a couple of DOS games with horrible magenta and cyan CGA graphics (even though my computer could do VGA, BTW): one was some kind of helicopter game that I couldn’t figure out how to play, and the other was some kind of side-scrolling platformer or beat-em-up (maybe Ninja Gaiden, or a rip-off of it?) that I also couldn’t figure out how to play.