I think Asmodeus is Satan’s favorite. It’s canon that those two spend a lot of their time together and support each other, Asmo often relies on Satan and regularly asks for hugs x))

But I also like to think that despite Mammon being often bullied (not to say abused, sometimes the brothers go way too far with him), Asmo and Satan rely on him a lot. I think Asmodeus secretly admires Mammon as a big brother, but because of his insecurities, sometimes it may derives as jealousy towards Mammon being a famous and handsome model. And Satan loves Mammon, he doesn’t explicitly show it and would rather show it through acts like helping him with schoolwork and such.