I can only offer personal advice, based on what I would do, but I’m happy to do so. Obviously, others may disagree, and I can’t guarantee success.
I look at utility. What heroes are gamechangers?
Justice, has AOE blindness (accuracy debuff which causes a lot of misses), and that seems to be much more powerful, as of late (although I think that was intended to be nerfed slightly with this update [1.5].). To me, that’s a game changer in Raids. I use Hu-Tao for the same principal, he’s just 4*. That AOE blindness debuff, if you can get it off in a reasonable amount of time, is DEVASTATING, and a game changer.
Rigard, is the best tank in the game, in my opinion, except maybe for Vivica. In my experience, Rigard and Vivica have been toughest to bring down since Boldtusks heal was nerfed by 5%.
Li-Xiu’s AOE mana drain is more effective than meets the eye. Triggering her multiple times prevents me from using me from using the special attacks I need to win, at a time where I need them the most.
Brienne has an awesome Attack buff which can be devastating, if she survives. A big “if”, because she’s a 3* hero that dies fairly easily at higher Trophy levels.
Some folks utilize pure damage output for defense. I’ve been able to thwart those teams effectively with Boril and his Perfect Riposte ability.
Skittleskull would be much better if his mana regeneration was a little faster and survivability was a tad batter. He’s one of those characters that I would argue is a little underpowered, but could easily become overpowered if he’s not tweaked carefully. His attack power debuff can also be a game changer. The problem is, it’s slow to generate and he’s fairly easy to snipe dead, before he has a chance to us ei.t
Sabina, I find easier to kill, in relation to Rigard. Not sure about the math behind it, as stated in a previous comment. It’s a little unclear to me as to why she dies easier, but definitely isn’t as threatening, in my opinion.
I can’t say much about Elena and Leonidas, as I’m not as knowledgeable about some of the 5* heroes as I probably should be.
Sonya, is… meh, at higher levels. She’s not wonderful. She’s not terrible. I used to have a lot of problems with her, but not so much anymore.
I hope this at least helps a little bit. Like I said, I don’t have all the answers, but hopefully I can offer a little bit of insight.
Cheers!
Avicious