Garou - Without Garou OPM isn't half as good, what more needs to be said? He took this manga to new heights. The way he mixes in raw tenacity and technique is a work of art. Usually characters like him ignore technique but he keeps it while going apeshit at the same time.
Zombieman - His demeanor is so calm/relaxed, and the fact that he tries his best to avoid upfront battles / prefers detective work even though he's unkillable. Just a boss all around.
Tatsumaki - She's such a bitch, but she has all the swagger and the power to back it, so it's hard not to like her.
Saitama - Love the way he goes about things, the end of the monster association arc really sums up and highlights his simple yet brutally honest character. This guy doesn't even know what's going on rn, only reason he's down there is to tell his neighbours to stop making noise, only reason he's even seen fighting is because he keeps getting attacked. A whole ass saga goes by with the Earth in trouble, and that's all this is to him, a knock at the door to tell his neighbours to settle down lmao.
Others would be
Metal Bat (this dude is essentially a gag on willpower, his fighting style makes no logical sense and I love it)
Amai Mask (an idol who is perfection infront of the cameras, batshit insane behind the scenes lmao)
Genos (because of his character design and fights, Genos always puts on a show regardless of the outcome tbh)
Silver Fang (mainly because he has the best looking fighting style, looks so pure and fluid)
I'm a bit similar to @Admiral Lee Hung in this regard. Can't say i've a particular favorite, but the ones who interest/interested me the most are Garou, Flashy Flash, Sweet Mask, Tatsumaki, Boros, Fubuki, Saitama and Silver Fang
> Garou because he brings a different aspect as anti-hero, aiming at making the villain win, while not being truly evil
> Silver Fang for his connection with Garou, as his former master, the relationship between master and student who went rogue
> Saitama because his existential crisis due to growing too strong is interesting and want to see what it'd lead to in the end
> Boros, was also similar to Saitama in a sense he had an existential crisis, growing bored due to becoming too strong, and lusting for exciting battles, also had interesting fighting abilities
> Flashy Flash because he is pretty smart, calculative, fast, while having a "training to achieve all" motto, actually similar to Saitama in a sense
> Tatsumaki because i'm interested by her psychic powers, and her personality is very fun, and arrogant
> Fubuki because i'm also interested by her psychic powers, but also because i want to see how she'd overcome her trauma of always being overshadowed by Tatsumaki
> Sweet Mask grew on me lately, with his behaviour not to go to the S-Rank to stop people weaker from the A-rank to go higher, despite clearly being S-rank worthy, arrogant as well, with his dynamic with the S-class heroes being funny to watch
Garou, Sonic, Suiryu, Saitama would be my favorites. Garou’s character is so well executed that even though he’s the antagonist, you lowkey want him to win instead, mans also got that underdog edge and I dig that as well.