This is really up to opinions and all vocals have strengths and weaknesses. ^_- Though I will say the worst Vocaloids are not as bad as the worst UTAU, but thats because the majority of UTAU are poorly recorded, whereas there is at least a standard with Vocaloid. To label a single vocal in either case as "the worst" overall is extremely bias.
However, in terms of the Vocaloid 2 generation, VY2 was the best male vocal hands down in terms of quality while VY1 was suppose to be the best female but this was the expectation of the VY series. You got a good vocal for your money, they were very professional voices. As the engine progressed Vocaloids generally got better, though this wasn't always the case.
SeeU's Japanese vocal is as bad as a 2008 Japanese vocal, this is the latest "bad" vocal but her Korean one is just fine. If I had to say which Vocals I like out of favourtism and what I tend to listen you. Tonio, Big Al, Oliver, Gumi, Gakupo are the most common I listen to.
I like English Vocaloids. I dislike Tone Rion and Miku, just because their vocal types I don't enjoy. But I won't label them as the best or worst because this is just what I like.
Having worked with Sonika, Prima, Big Al and Tonio, Sonika is the only one I don't like working with, while Tonio's is my favourite singing results but Big Al the better Vocaloid. Prima is a nice singer all round.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.