Well I guess it's also because both Huey and Fenton are such loveable, comedically, dorky(not meant as an insult), nerds that just make me smile and laugh. Plus there are some things for both of them that I can really relate with.
While with Dewey and Launchpad, they're both loveable and funny, but I can't relate with them as much. And as for Louie and Goldie I can't really say much about them because they only had one episode where they showed loyalty and compassion for each other while the others had many.
