Altema updated their top 10 if you're interested in that
https://altema.jp/dffoo/saikyo-611?utm_source=最強&utm_medium=Gナビ&utm_campaign=Gナビ
1) Ultimecia
2) Rosa
3) Emperor
4) Warrior of Light
5) Zack
6) Y'shtola
7) Ignis
8) King
9) Rem
10) Setzer
Remember those rankings are voted by the community so it can be highly subjective, also anyone with EX+ is going to be good for CHAOS.
6. Y'shtola is just such a powerful all-round support! She delay's enemy turns while dumping, she batteries 120% her own Current brave, while providing MaxBrv buff and, most important of all, she has the most powerful Support EX in the game, healing Hp Without cap, Reviving, providing maximum brave, buffing her own Max brave, providing Regen, making her HP attack battery herself, dump, then battery her allies by half the damage dealt, passively keeps her from dying at 50%+ Hp, and the kicker is, IT'S A FREE TURN! Best in emergencies, great general use!
7. Ignis has many support options, and can switch between defense and offence aura's with his second ability, batterying his allies along with a free turn to choose it's effect!. Memory lane Pastry provides a ton of atk and MaxBrv overflow, and Bird Bowl gives Hp Regen and Debuff resistance, while providing unique Brv+ and Hp+ for both that usually raise party brave in some way. His EX batteries everyone, then it does HP damage based on the party's Brv, then immediately let's them act, even letting you control who goes first, coordinating a powerful follow up! Plus first ability heals everyone based on max Hp and provides party atk and max brv buff
8. King just can't stop attacking! He only needs to use one ability to deal four consistantly high Brave hits and an Hp chaser, and his EX, though slow, does lots of damage three times, with massive overflow, and a powerful self buff! His second ability complexity refreshes his first, while providing party battery, and HP attacking, making every turn he takes simply a turn full of damage. Plus Crazy longevity due to ability refresh and Free turns with break.
9.Rem provides a very unique level of turn control, simulatiously buffing herself and a single ally with Max Brv and Speed, providing both battery, expending no turns of her own in the process, and immediately switching places in turn order with them. She can therefor be incredibly efficient in providing her two allies with all the flexibility necessary to preform devastating combos otherwise too difficult to leave to chance. She also dumps brave and batteries effectively, can heal everyone and provide an Atk buff, and her EX deals tons of Hp damage while providing healing and battery. Plus longevity with Free ability after EX.
10. Setzer lives up to his name as a gambler! Even with low ability uses, he provides massive utility and longevity with his EX and careful ability use. His first batteries himself and his allies massively, does a single powerful brave hit to all enemies, shared HP damage, max brave buffs everyone, and Freezes enemy brave gain for 2 turns, completely denying enemy HP attack damage. His second ability hits with three brave hit plus HP attacks three times in succession, finishing with turn delay. And his EX provides battery to everyone (but the one with the most brave, for some reason?), does a ton of hits, and provides an Aura buff that raises max Brv and Atk for everyone, especially himself! Plus longevity with Brv++ and Hp++, and his EX charges very quickly.
I hope I gave a good rundown on why people are loving these characters in Japan, and I hope this provides good context for future pulls! Go for your faovrites if you like, just know that none of these character are the best, unless they work together in a team that makes the most of their strengths!
And most bosses will deny certain strengths, and be vulnerable to certain strategies, so try to space out who you want to get so you're prepared for any situation!