Least you can burst Attuma with Herc with little self damage, specials also short and easy to avoid. Korg tho, that boy is something else with his goofy ahh sp-1 random pew pew beams.
If you’re paragon I say rank up both as 6*s since rank up materials are easier to come by than 7* shards at the moment and it still could be months before you pull either as 7*s
Attuma is much easier to fight and counter.
If I have the right team, I can beat Korg, if not, he wastes me. Attuma is tricky, but figure him out and you can beat him with anyone.