I have been testing just about every character since I got this game 2 weeks ago and now I think I've finally settled on a main.. Scorpion. He's my main from MK1 and I've always had a soft spot for that Spirit of Vengenance (Scorp's got many similarities to Ghost Rider now that I think about it)
But when I first got the game I wanted to try Black Adam right away because he's such a badass and his moves are flashy and cool looking, but after giving him a try in the lab I didn't like the flow of his game, and after dabble a bit in Aquaman I decided to try Superman.
Superman is a lot of fun to play for me. I like how versatile he is at zoning and mix up and he's got answer for just about every type of fighter in this game. I was able to get his 1,1,1,scoop>mb breath>b3,j2,d,df2 combo going and tested against Med difficulty AI, but all this time I keep thinking I don't want to just main him before giving other fighters a chance. So I started playing the following:
Bane
Sinestro
Catwoman
Flash
Killer Frost
Solomon Grundy
Nightwing
Green Arrow
Green Lantern
Ares
Hawkgirl
Deathstroke
Wonder Woman
Batman
Batgirl
Lobo
Raven
In other words, pretty much the whole roster save for a few. Ultimately none of them really appealed to me. My mains in other fighting games are Kung Lao (MK9), Fei Long (SFIV), Kazuya/Akuma (SFxT) so I favor aggressive fighting style mostly. Maybe that's why Superman isn't my main despite spending so much time in the lab with him. For now my main is Scorpion and alt is Superman until further notice. I will see what other DLC fighters will be before deciding whether to stick with these two or not.