I don't have any one favorite, but i can name some that i like a lot Miku-Kucchi Muite Baby Rin/Len-Revolution Miku/Gumi-Matryoshka Luka/Gakupo-Kiss Kaito/Len-Erase or Zero Miku-Last Night, Good Night Meiko-Akuzikimusume Conchita Len-Butterfly on Your Right Shoulder Rin/Len-Synchronicity Okay, so that's more than a few, but i think they're all really good songs