I love Chara because I kind of relate to them. Honestly, every character in Undertale is relatable in some way, and that's great. I honestly can't say that I hate any character completely.
Like, there's every reason to hate Flowey, but I find it hard to imagine to not feel at least a bit bad for him after finishing the game. I can't even imagine being in his shoes... er, soil. (and I love him as well)