…None of them
They aren’t even getting head
The truth is, the chipmunks are Ultra Virgins. They are so virgin that their own girlfriends refuse to do anything sexual with them. But Alvin, being the kind of person that he is, wanted to make it seem like he and his brothers were chads. So he commissioned Simon to upload the original “Which Chipmunk is getting the best head” meme. And his plan worked, so we all thought they were getting head, and tried to figure out who was getting the best head, when in reality none of them were getting any. They played us like a damn fiddle