What, in your opinion, was/is the greatest Free to Play game?

I have played a few over the years, but I don't think anything brought me as much joy as Marvel Heroes. the diversity of characters, the fact it was decently balanced. Only problem I have with it was the comic prestige thingy. I did that with Scarlet Witch and said never again. That was a chore to say the least.

I also really liked Maplestory back when I was in highschool. Annoying other players with my dexless sin was always fun. But sadly the MTX hell hole it turned into breaks my heart.

Though, thinking back on this, I think I would love Maplestory 20 years ago more than Marvel Heroes coming back, but only by a little.

What Free to Play games rubbed you the right way?