The way he feels about them are so different it’s hard to compare them.
I wouldn’t say Joker necessarily loves Batman. I think he’s grateful for Batman for the life he provides Joker with. Joker gets to prove himself the greatest villain, gets to showcase how clever he is, and gets to have so much fun all because of Batman. But who Batman actually is, what he stands for, his beliefs, Joker hates. He hates those things. Being evil is better. I think Joker thinks himself the most evil, and therefore the best opponent to fight good, and Batman the most worthy opponent for good. So in Joker’s mind, they have to fight. Evil has to win. They are enemies. But all those affectionate things Joker does to Batman, he means it, because he’s genuinely grateful for Batman’s existence. He’s obsessed with him, and he’s grateful for him, he loves the life he has with him because he gets to showcase himself because of it. All Jokers feelings for Batman can be rooted to his ego. There’s no real love.
But I think Joker genuinely loves Harley. But he represses those feelings. He gets angry about them. He hates them.
So for genuine real human love, that goes to Harley. But who gets the strongest positive emotion? Who makes Joker happiest? That would be Batman. In the end, for Joker, its all about himself. And Batman allows Joker to do what he does best, and be the most evil the best.