We made this game, Pengbears, using Unity and 2D Toolkit. All the images in the games are 2dtk sprites.
What I like is how you can make sprites and add different kind of colliders to them, like the polygon collider.
You can try the game for free here:
https://play.google.com/store/apps/details?id=com.kelson.pengbearsFreeIf any questions, let me know