Personality, character traits, principles and standing by those is what's most important. Then you need power level and design. I think the fandom divisions are because different personality traits resonate with different people at varying degrees. Some times there are certain moments which can propel a character from being the worst to one of the most popular.
Take Momo for example, since his introduction I think he was one of the most loathed characters in the series, annoying little kid with bad design. However, Wano and Onigashima explained his personality, he had a few character moments but the biggest one was him taking the risk and sacrificing 20 years of his life. Then we get the cool design and obvious powerlevel potential with Oden body, Kaido fruit, VOAT too. I don't think Momo even has a fanclub here.