My most fun admittedly are amoral characters or ones with a few nasty and ugly personality traits. They are a good contrast with more typically benevolent ones if needed. They tend to disturb the other characters and throw in a lot of questions that are fun to work with. >
Kind-hearted and "fun" people that are caught in a moral struggle. I've read about some of these characters "He's a good person yet doing awful things" and I think that sums up what I mean. Roy from Fullmetal Alchemist is one example for of these characters.
Also more introverted and ruff around the edge characters that aren't your typical edgelord or macho type. Characters like Geralt from The Witcher. He comes off as ruff, but he's empathic towards the poor people who are giving him quests and their tragedies, he cares for the women in his life etc.
Jaheira from Baldur's Gate is like a female interpretation of this, I think and I love Jaheira as much. xD Or Vi from Arcane.
In general I like kind-hearted characters that aren't "too good to be true" and aren't this kind of show-off empathy. They should feel genuine and human. The empathy of characters like Tanjirou from Demon Slayer is way too much in your face, but like... I felt everyone in there is so annoying and dropped the anime.