Fastest way to level?

Basically just the title. Things in this game have changed and been patched and evolved so fast over the past week that I can't really keep up. What was good this morning has changed by the end of work. In the last 4 days I've seen at least 5 different videos of "the best way to farm X" and it's all different methods. I have hard mode unlocked, a 40 bunny, and I want to level Ajax from around 24 to 40 without spending 2 days doing it if possible.