at the moment, there currently aren't any vocaloids i'm absolutely opposed to. that was different in the past, but i think this change came when i started actually using vocal synth. I can appreciate them all in some way or another now, and i'm happy that i'm able to say that today.
I remember disliking Kaito a ton until I heard this song. eventually I listened to more of Shinjou-p's Kaito stuff, eventually more Kaito v1 stuff in general, and now i appreciate kaito in all forms. i still think his v1 has a certain charm that i love, however.
Now, i wasn't here nor there for Maika for a while. I wasn't too interested in Spanish vocaloid personally, though i still appreciated it. it wasn't until i listened to Define Me by Nostaightanswer, and heard how great she sounds with english, she was almost immediately brought up into my top 10 or so!