I keep a regularly updated backup version of my personal favorites and some of my friends' banks. These include each version of my UTAUs, which is Shadow (CV/VCV Dusk, Dawn, and Base), Ruka (CV/VCV), Neko, Storm, Snow, Star Wilson, Kevin Andrews, Aero Andrews, Sora Hoshiko (Main/Alt), Elian Song, Vincent Song, Taro Akumi, Hanako Akumi, Haku Akumi, Ryoko Yumeko, Ace Yumeko, Helena Yumeko, and Kian Walsh. Then it has Etsuko Akane, Kokone Kara, A0N, Lei, Aimi Hakune, Michiko Akane, All of Matsudappoiyo's voicebanks, all of Matsudappoine's, and Akuta's.
Then the ones I don't have backed up I'd go for Ruko's voicebanks, Ritsu's, Teto's, and Rook's. Maybe Momo's..... I don't have Momo's as of now.