Based on what we know so far, Superman and Nightwing.
Superman - really like his main costume, looks fairly easy to use, and gotta like at least one "Power' type Nightwing - really like the character, design is near-perfect, multiple fighting styles, and fills the "Gadget" niche
Harley, Nightwing or Raven (if she's in the game) Honestly, they're just three of my favorite DC characters. Also, Nightwing looks like one Hell of a character. So stoked on how it looks he's turning out.