To be honest, I'd have to say Maple Story.

The height jumping, mass grinding, the small bodies (You pay 5$ for shoes you can't even see!), too many people (For my liking), AoE attacks are skill based (In LaTale, a basic attack could hit 3 monsters, hard attack hits 5), and the general game's graphics are unappealing to me.

I found WonderKing and/or LaTale to be much better than Maple.