shoshinsha
Apprentice
If you've not read comics in the last couple of years (since the reboot), then your info on the characters is going to be off, because a lot of characters are being handled differently than they were previously. I'll try to give a pretty current tier list, with a few explanations where necessary. Note that some characters are so radically different from their Injustice appearance that we pretty much have to use their previous incarnation or else we're not talking about the same characters.
S+
Ares - This guy is a god. In the comics, he's just head-and-shoulders above everyone else here.
S
Martian Manhunter - Even the previous version of MMH should go here, and the newer version is far more powerful. The previous version went bad and beat up the entire JL simultaneously, INCLUDING the more powerful Flash (Wally West). The new version's weakness to fire is much lower (it's a psychological thing, like PTSD, and is specific to flames, not heat or lasers or anything). He's single-handedly fought the JL, been selected as the guy to take down Superman if needed, mindraped Despero, and more. He's also much more ruthless and amoral about using his powers.
Wonder Woman - She's gotten a huge promotion. She's as powerful as Superman, and when she takes her bracelets off she basically goes Super Saiyan. No weaknesses + godly magical weapons. If she had any mental powers she could go even with MMH.
A+
Black Adam - As powerful and ruthless as ever.
Shazam - Same power as Adam, but not as smart/experienced/ruthless.
Superman - As powerful as Adam/Shazam, but now he's actually weak to magic like he is to kryptonite, so he can't hang with them.
Zod - Not much known about the new version, but it doesn't seem like much has changed.
Doomsday - New Doomsday is a weird, terrible aberration of the old version. Old version was only ever the Superman-killer in his first couple appearances though. He lacks the versatility to hang with anyone who knows what he can do.
Lobo - Ridiculously strong and unkillable, but kinda derpy and limited in versatility. There's also some new version of Lobo who's supposed to be the "real" Lobo, but he's all skinny and emo-looking, so I'm pretending he doesn't exist.
A
Sinestro - Smarter and more experienced than GL, IMO.
Green Lantern - Powerful, but tends to get KO'd by the folks in A+ tier.
Zatanna - Super powerful, but human-like vulnerability.
Flash (Barry Allen) - Everyone thinks of Flash and remembers the crazy-powerful stuff Wally West did. Barry Allen has not done that stuff. If this was Wally, he'd go in S tier. Barry, however, is just the fastest guy on the list and also has some nifty tricks and gimmicks. I miss Wally.
Aquaman - He kind of belongs in the middle of A and B+ tiers. Very strong and skilled, but he doesn't have the power versatility. If he has Poseidon's trident like he does in Injustice (but not in comics), then he belongs with GL.
B+
Deathstroke - The Batman of supervillains--but smarter, stronger, and more ruthless.
Lex Luthor - Lex has recently shown himself to be pretty goddamn smart in the New 52 and, though his power suit doesn't seem as powerful as previously, he handles it well.
Cyborg - Theoretically very powerful, but gets no-sold too much to be placed higher. Mostly useful for tech support.
Raven - Again, theoretically very powerful, but too vulnerable and inconsistent.
Hawkgirl - Like Aquaman, really belongs between this tier and the next one down.
B
Joker - Actually seems to be able to beat Batman in both fighting and planning, now. Not sure if that will stay consistent.
Batman - Everyone knows Batman. Realistically, his plans don't save him from everything.
Catwoman - Has been up-played as a reasonable foil for Batman lately.
Bane - Not much different than previous version. Isn't going to beat Batman without the element of surprise.
C+
Killer Frost - A relatively-high-powered villain who's treated as pretty generic.
Solomon Grundy - Very inconsistent, but lately nothing special. Has previously been able to stomp the entire JL.
C - Everyone in this tier is pretty much "good fighter, not that special."
Nightwing
Batgirl
Green Arrow
Harley Quinn
No-Comic Tier
Scorpion
S+
Ares - This guy is a god. In the comics, he's just head-and-shoulders above everyone else here.
S
Martian Manhunter - Even the previous version of MMH should go here, and the newer version is far more powerful. The previous version went bad and beat up the entire JL simultaneously, INCLUDING the more powerful Flash (Wally West). The new version's weakness to fire is much lower (it's a psychological thing, like PTSD, and is specific to flames, not heat or lasers or anything). He's single-handedly fought the JL, been selected as the guy to take down Superman if needed, mindraped Despero, and more. He's also much more ruthless and amoral about using his powers.
Wonder Woman - She's gotten a huge promotion. She's as powerful as Superman, and when she takes her bracelets off she basically goes Super Saiyan. No weaknesses + godly magical weapons. If she had any mental powers she could go even with MMH.
A+
Black Adam - As powerful and ruthless as ever.
Shazam - Same power as Adam, but not as smart/experienced/ruthless.
Superman - As powerful as Adam/Shazam, but now he's actually weak to magic like he is to kryptonite, so he can't hang with them.
Zod - Not much known about the new version, but it doesn't seem like much has changed.
Doomsday - New Doomsday is a weird, terrible aberration of the old version. Old version was only ever the Superman-killer in his first couple appearances though. He lacks the versatility to hang with anyone who knows what he can do.
Lobo - Ridiculously strong and unkillable, but kinda derpy and limited in versatility. There's also some new version of Lobo who's supposed to be the "real" Lobo, but he's all skinny and emo-looking, so I'm pretending he doesn't exist.
A
Sinestro - Smarter and more experienced than GL, IMO.
Green Lantern - Powerful, but tends to get KO'd by the folks in A+ tier.
Zatanna - Super powerful, but human-like vulnerability.
Flash (Barry Allen) - Everyone thinks of Flash and remembers the crazy-powerful stuff Wally West did. Barry Allen has not done that stuff. If this was Wally, he'd go in S tier. Barry, however, is just the fastest guy on the list and also has some nifty tricks and gimmicks. I miss Wally.
Aquaman - He kind of belongs in the middle of A and B+ tiers. Very strong and skilled, but he doesn't have the power versatility. If he has Poseidon's trident like he does in Injustice (but not in comics), then he belongs with GL.
B+
Deathstroke - The Batman of supervillains--but smarter, stronger, and more ruthless.
Lex Luthor - Lex has recently shown himself to be pretty goddamn smart in the New 52 and, though his power suit doesn't seem as powerful as previously, he handles it well.
Cyborg - Theoretically very powerful, but gets no-sold too much to be placed higher. Mostly useful for tech support.
Raven - Again, theoretically very powerful, but too vulnerable and inconsistent.
Hawkgirl - Like Aquaman, really belongs between this tier and the next one down.
B
Joker - Actually seems to be able to beat Batman in both fighting and planning, now. Not sure if that will stay consistent.
Batman - Everyone knows Batman. Realistically, his plans don't save him from everything.
Catwoman - Has been up-played as a reasonable foil for Batman lately.
Bane - Not much different than previous version. Isn't going to beat Batman without the element of surprise.
C+
Killer Frost - A relatively-high-powered villain who's treated as pretty generic.
Solomon Grundy - Very inconsistent, but lately nothing special. Has previously been able to stomp the entire JL.
C - Everyone in this tier is pretty much "good fighter, not that special."
Nightwing
Batgirl
Green Arrow
Harley Quinn
No-Comic Tier
Scorpion