You know, I'm getting sick of comparisons between the two, not because their being compared, but what their being compared for. I don't know, but I've yet to a UTAU sing a song that a vocaloid couldn't do better. But you can't say this to a UTAU user without them trying to prove you wrong. Its like the Engloids troubles back in Vocaloid2, trying to prove they could produce realistic results alone was a bitch as half the VO forum itself was convinced there was NO WAY they could ever "sound as good as a Japanese vocaloid". :-/
VO has matured in the sense its leap away from this and aside from a few trolls around the fandom things are quieter. Now its UTAU users that are starting to get a bit annoying. I'd like to say "look UTAU users, your software is good, its just vocaloid is better, UTAU has things which Vocaloid can't do but when it updates it raises the stakes you have to climb. You had triphones two years before vocaloid had it... So what? When vocaloid3 showed up it meant squat because the engine was better."
Plug-ins? We've got them now too! And the average Vocaloid is STILL better then the average UTAU.
In the process of UTAU users trying to convince me their software if better, I often witness them becoming blind to aspects of UTAU, just the engine noise along is worst in UTAU then Vocaloid. I'm getting pretty bored out of the UTAU users lately, especially since Vocaloid3 and I often think their becoming more retarded (meant in the medical/old fashioned sense and not the modern term to imply one is stupid), its sort of like explaining to someone how the average Vocaloid sounds flat. Unless they "get" what you mean its difficult to explain. :-/