In my personal experience and opinion, the most problematic for me so far have been:
Aquaman. ....
Superman. ....
Nightwing. His staff stance gives me trouble. He has a really fast d1 thats plus 1 on block, and his ranged pokes 1f1 thats also plus 1 on block I believe. He has a faster d1 than arrow on escrima stance, and his d12 is also plus on block and sets you up for a frametrap. I find it difficult to approach him or start any offence, especially when he's in staff stance. he has so many frametraps! And from full screen his db2 in staff stance (the ground spark) is hard to counter. If you load he hits you, if you try to fire an arrow it beats you. So you have to respect it. Jumping doesn;t seem viable, especially with Arrows floaty jump. The method thats worked for me is dashing them. If you time it right and you read he's going to do one, you can dash and the spark won't track, you actually see it hit behind you. I'm at a lost in this matchup, don't know how to fight him yet.
Black Adam. ...
Cyborg: I can handle him from mid range and close but getting in is the problem. I can't counterzone him, lose every trade, and when I do inch my way in, he grapples the fock outta there with his armored grapple trolololo. Whats the secret to beating this character with arrow, besides patience and hella good reads?