I'd say Irelia, Tristana and Teemo.
Irelia: a great solo top, Melee, Magic and true damage a free heal, what's not to love?
Tristana: fairly easy to play, insanely effective ADC. Also.. she's free, so.. yeah.
Teemo: ALOT of people hate Teemo, honestly I don't know why... AP teemo is crazy easy to play and super effective..... Ya know when I see it written down like that I can kinda see why people might not like him