>>725244561
Purely by time spent, the flash implementation of the Gem TD map from warcraft 3.
The creator rebuilt it in javascript so it still runs without needing a flash emu, and it's been my mental fidget toy for a decade or more.
>gemtowerdefense.com
no I'm not shilling, the man doesn't even take donations for his tiny webhosting, I'm just glad a decent TD like this still exists in a format I don't need to fire up WC3 Deforged to play.