I wanted to give my take also to a DC rivals game because I really like the concept. What I liked about Marvel rivals is that they didn't hesitate to add B-tier Marvel heroes, and I try to replicate that in my roster. I also tried to add characters that could have ranged attacks in some way because I don't want this to be a brawler (although a few characters use more close range combat, like Marvel rivals having Iron fist, Magik and Psylocke). So here's the roster:
Vanguard
Superman: Very obvious pick, not a lot to say here. I guess you could make a case that he could be duelist, but I think it make sense to have him a close range tank character, but he could also use his lasers for ranged combat.
Shazam: He could have a gimmick where Billy Batson could fight in some way.
Green Lantern: Another obvious pick, I think he could create walls to protect allies and fight using energy blast or maybe he could have some kind of construct gun to feel more like a typical hero shooter character.
Swamp thing: He would be very similar to Groot, where he could summon trees and natural stuf to slow down enemies and create walls.
King shark: He would be a high mobility tank, he could swim to reach enemies or go back in the backline, I imagine his play style a bit similar to Ball in Overwatch.
Lex Luthor: I'm surprissed he's not brought up by KneeofJustice or AlRex. He feels like a very obvious pick to me, being able to tank damage with his big armor. He could also have a gimmick where he could fight a bit outside of the mech similar to D.Va.
Vixen: I originally had Beast boy, but I wanted a female tank, so I go with her. She could take the form of big animal to be a tank.
Stargirl and STRIPE: I originally had Stargirl in duelist, but I figured her powers weren't super original, so I went back and forth with her, and when I saw that AlRex had them in post launch characters, I decided to add them this way.
Duelist
Batman: To me Batman feels more like a dualist, he could throw batarang around and also place traps on the maps.
Wonder Woman: You could argue she could work as Vanguard, but I think her shield is too small to really work that well in that category. I imagine her similar to Overwatch's Brigitte. She could use her shield to get in close range, and fight using her whip and sword.
Aquaman: Would pretty much work like Namor, where he would throw his tridents and summon aquatic creatures to help.
Cyborg: Not a huge fan of Cyborg personnally, but he just make a lot of sense for this type of game. He would be the basic easy to pick up hero.
Green arrow: He would be your typical long ranged fighter.
Blue beetle: He just make sense to me, with his energy canon and all the stuff he can do with his suits.
Black Canary She can fight using her sonic screams and martial arts for close combat.
Raven: She could fight long ranged using magic, and summons creatures to help her and her team fight.
Static Could throw electricity and stuff
Starfire: Again, pretty straight forward hero that could shoot energy stuff.
Hawkgirl: She could fly around and throw her mace
Harley Quinn: I originally wanted Joker, but I agree with KneeofJustice that she makes more sense in this type of game. She could fight mainly with her popgun, but also other gadget.
Nightwing: He would be the short range duelist of the game, jumping around and attacking with his stick.
Lobo: He could hook people and fight using his shotgun. You could argue he could be a tank because that's how Roadhog work, but I don't think he's quite big enough to really go that way. I think duelist fits him more, and he could maybe even use his bike in some way.
Peacemaker: He would also fight with a shotgun, but also use his helmet for longer ranged attack.
Mr. Miracle: He could shoots energy blast with his glove for long range, and also fly around the stage.
Sinestro: I felt like the power rings have a lot of moveset potential for this type of game, so I decided to throw Sinestro there. He would be a more agressive version of Green Lantern, having construct that focuses more on direct combat than defense.
Grail: Alright this might seems like a weird pick, and I assume many people wouldn't even know who she is, but I wanted a more recent DC characters, in the same way that Marvel rivals had Jeff the land shark, Peni Parker and Luna Snow. Grail is the daughter of Darkseid, and she fight using a scythe, and she also have some of Darkseid powers like the Omega beam. I imagine her similar to Magik, just a badass fighting with her scythe, but Omega beam could also be used for ranged combat.
Strategist
Zatanna: She would give debuff to enemies and buff to allies, alongside attacking.
Constantine: He could summons demons that would buff his teammates.
Doctor Fate: You might argue that's a lot of mage, but I think Fate has unique potential, because he could have a gimmick where he could "predict" when a enemy is about to ult by having a indicator when someone have full ult charge. Also he could heal and throw magic spell.
Poison Ivy: Could give debuff to enemies by summoning plants.
Rebis: Not a lot to add here, I just think it's a genius idea.
Forager Could give shields or other gadget to his teammates.
Dex-Starr Yeah this is the weird one. I wanted something similar to Jeff the landshark, and while he's far from being cute, I think playing as a flying cat is funny enough to give him a spot. I out him in suport because he could create small shield to allies or throw acidic vomit on the field to do small damage in a zone.
