Based on my experience so far with the character and what characters I've played against him,
Flash sub- 4-6 (can lame flash out all day and corner traps him easily. No punish for clone cancels)
Deadshot sub- 6-4 (this is not the worst matchup, especially if you can corner deadshot, it's just a patience thing. And slide is helpful)
Superman sub- 5-5 (some tell me sub wins this but I think it's a 5-5. Zoning is annoying for sub but superman gets stuck in the corner and really no punish for clone cancels. The mid lazer going through clone is bullshit tho)
Adam sub- 6-4 (everyone says it's a 5-5 and it's prolly right, but from my personal exp, Adam is a nightmare to deal with)
Lantern sub- 5-5 (haven't played this much, but lanterns zoning is weak and his wakeup can be whiff punished in the corner)
Beetle sub- 5-5 (prolly one of the more fun matchups to play as sub imo. Does well against beetles zoning if you're patient enough and match is even. Sub can escape fly cancel pressure for free too
Bane sub- 5-5 (can be sort of lamed out, if you understand how to escape banes dumb shit that is, and traps him in the corner decently. Read heavy game)
Batman sub- 7-3, (one of the worst, trait is so anti clone you can't defend yourself. Shit anti air so jumps are free, and you need to pushblock so more meter usage on already meter intensive sub. And also batman can zone him).
Aquaman sub- 7-3 (everything this character does has no hitbox, it's like fighting alien again. Pretty self explanatory. However sub has a great answer to his trait and slide punishes ftd midscreen)
Others I'm not sure about (mostly speculation and some sets with avg players)
Red hood, 5-5
Starfire. 5-5
Catwoman, 5-5
Supergirl, 5-5
My thoughts on sub: he's decent and with good reads he can work, but he does need fixes to his pressure and his strings and some buffs like d1 special etc