Board Thread:Questions and Answers/@comment-148.109.1.11-20131219190545/@comment-5051846-20131220093715

Vocaloids which I know are difficult: Mew, Sonika, Miki and the Kagamines.

Vocaloids which I hear reports about them being easy: Iroha, Miku, Avanna

Hopefully that helps you a little.