Heroes of Newerth. LoL is a disease of a game if you want to move into Dota 2, you will learn a lot of bad habits and playstyle.
League of Legends is based on casual players who just like killing other players, the only reason it has a 'competitive' scene is because the amount of money Riot have backed into tournaments.
Playing HoN will grant you better knowledge of items, heroes and mechanics which will help you switching to Dota 2!
For reference, I'm not saying LoL is a terrible game, It's a pretty fun game but it's a disease for any person wanting to switch into Dota 2.
Add my smurf account on HoN if you want to play: Astaeri.