I love Sharpkey and I'm psyched about SiVo, but those won't let people import their own UTAUs just yet (if ever!)
I'm excited to see how VOCALUTAU works if it ever comes out!
Sharpkey. It sounds really good as far as quality goes, and the interface is pt tight. It is intuitive and user friendly and doesn't seem to distort voice quality as much as other synthesizers.
UTSU most definitely! Sivo and Sharpkey are just new vocalsynth projects, entirely independent of UTAU. UTSU is actually made for the purpose of being a multiplatform frontend for existing UTAU resamplers and voicebanks. The developer made an UTAforum thread about it here: http://utaforum.net/threads/utsu-a-cross-platform-vocal-synth-frontend.17476/