I like the main trio and Makima.
Makima is an obvious pick. Unrepentant, threatening, and a force to be reckoned with. Basically, she is everything Meme and Crydo are not.
Aki is a subversion of the brooding vengeful emo ala Sasuke (who was endlessly boring). The chapter where he took Denji and Power to visit his family's grave but ended up not getting the chance to feel sad thanks to Power and Denji's antiques was a riot. I also like how Aki's journey does not follow convenient shounen tropes and proves that the author is ballsy as fuck.
Power is selfish and funny, but her relationship with Nyanko is wholesome and her dynamic with Aki and Denji is heartwarming. If something happens to Nyanko, I'm participating in Ragnarok to duel Anubis and get Nyanko back, btw.
Denji, especially, since he does not aspire to greatness. Very often that shounen main chars aspire to be no. 1, but Denji is content with aspiring to have a normal life, and that's relatable as hell. Not all of us want to be the Pirate King and repeat it a trillion times. Some of us are content to have a cool job (and salary), a nice home, and a loving family, like Denji. His personal dream kinda reminds me of Zoro's.
OOT, but Denji and Zoro remind me of the MC of a recent manga, Kaiju no. 8, called Kafka (maybe you've read it) in the fact that their dreams are personal and not world-changing, but they have to move heaven and earth for their dreams. They are all flawed yet engaging. Naturally, K8 is a manga on the path to greatness.