First: Harley - Overall a well-rounded character, not overwhelming at all if you know the MU.
Second: Raven - Fanboy main. She's a zoner, which I don't really like doing, but she's awesome. So it's 'kay
Un-decided: - There are so many people I want to play as. Flash, Cyborg, Catwoman, Killer Frost, Bane, Joker...
Third-ish: Doomsday (for now) - Pressure machine. Feel like a badass every time you win. "I will destroy you all"
I tried to make it similar to my MK9 mains. The only difference being is Reptile is a jack-of-all trades, and Raven is a zoner. Still fanboy mains though.
Liu Kang
Reptile
Johnny Cage