In my opinion, I tend to use an UTAU because of the voice, mostly. I listen to quite a few of covers on Youtube, and normally the quality of an UTAU's voice is what calls my attention. I also try to listen to the voice and not focus on the art (because sometimes the design of a cover was drawn on Paint, and let's admit it may not look great), because I think an UTAU must be recognized by it's voice.
I also do a few requests, when a friend asks me to make a cover with a certain UTAU (which doesn't mean it's their own). I think it's nice to try and get the most out of a voice (sometimes, the right flags can make miracles!).
About owners, I try not to hold anything against any. UTAU is a community, so it should act as such. Of course, if a person is being reportedly mean/jerk/assh*le, they don't deserve the attention. But sometimes we may think an owner is a jerk, and in fact we don't know them enough to actually KNOW if they are a jerk. Sometimes a misunderstanding may lead to bigger and unnecessary things (it happened to me). That's why I try not to hold anything against owners. I think that talking we can get to an agreement.