To me, it depends on how the voicebank is configured. Sometimes, some UTAUs have voices that are considered unacceptable (not cutesy, mot manly, whatever) but have a decent (or slightly, at least) oto.ini file. Mine included.
Based on my past experience, I used a few VBs with low quality, such as Izumi Kio and Aru (CyanOnigiri's UTAU). Their VB oto.ini are slightly decent but the voices are too deep, making me feel slightly hard to mix their voices.