I like them all but miku is my fav one so I love her more but it doesn't mean I don't love the others.

For me, it's that people don'y just judge by music but sometimes personality also. I look (and make) a lot of MMD, and unknowingly, people don't notice they had made personalities for the Vocaloids until it's too late. What I mean by too late isn't negative, but the stage that most people now generally see that particular Vocaloid as Nice and happy (Miku), A bit perverted (Len/Kaito), motherly (Meiko, but she is also known as an antagonist sometimes too), and etc. Yea Miku takes the spotlight a lot, but the more popular the character is, people can't help but pull out that person more, cuz most people will want Miku more than the others. Then you have the other (Not liking Miku as much) people that's like, "Wait, why is she so popular, Rin can do just better.." or something like that. I call it being normal.
Of course there about a million other reasons, but I'll just talk about one other reason, one other form is the artist interpretations of the Vocaloid. A good one is Hatsune Miku's pretty well known song Love is War. If you search images of Hatsune Miku in Love is War "mode" she looks pretty cool and what people say these days- Epic.
But then if you look at a scene of Hatsune from say... Melt, she seems like a cutesy, type of girl that sings about a guy. It's usually just about opinions, we like different things from our Anime-like singing idols.
To me, it makes sense if you don't like Luka or Rin or any Vocaloid, I mean people have their own thoughts and feelings. About Vocaloid peace, I actually prefer there be some dispute because it keeps BSers and critics like me something to do, but I do believe there cannot have a HUGE riff between the Vocaloids, even between Vocaloids and UTAUs, All of the Vocaloids and UATUs took a lot of time and effort to make the voice banks for every single one.
I (somewhat) successfully produce Vocaloid music and I have to say, don't just go off because the Vocaloid doesn't sound right, or "feel" right. It's a backbreaking job for the boys that made them. ( I know I'm wandering off topic)
Bottom line there is no better vocaloid. There CAN be a better song, but I recommend not to decide that quickly though. There's some good songs out there from every Vocaloid. So there, that's my 6k cents on this topic.
[And yes, know I BS a LOT.]

I love Hatsune Miku and nobody can chang my mind at all. MIku is one of the best popstars ever im so in Love with Hatsune Miku right now. So don't let aneybody tell you that Hatsune Miku is lame cause shes not lame is is awesome way past cool. I really love Hatsune Miku alot :D i give Miku haters no respect at all.

Miku is favorite, I will say that. But of course I love other Vocaloids too. Like Luka! I just loved how she sang Just Be Friends and Magnet (with Miku). Miku is not lame, she is awesome. Just because Miku is ontop does not mean you have to hate on her. You should actually be Thanking her! She was the one who made Vocaloid popular.

I have to say, I disagree a bit. If we like a certain Vocaloid, I don't see how that means we should like another for that simple reason. Perhaps we don't like a certain Vocaloid's voice. I like a lot of music that the Hatsune Miku voice banks has been used for, but as the voice, itself--not so much. I find it to be a nuisance more than anything else. For me, it mainly depends on the quality of the music that they are being used in, and not the Vocaloid, itself. They aren't real singers and don't create their OWN music. Anyone can purchase the software, and that is why the Vocaloid music varies so much. Some music is beautiful because of the lyrics and melody, such as "Desert Butterfly" by monaca:factory. Some Vocaloid music is considerably terrible because the lyrics are so stupid; for example, "World Is Mine" by supercell. I don't see why their are rivalries in Vocaloid, though. I agree with you on those terms, for sure. Personally, I respect Miku "haters" more than the fans, despite that I like Vocaloid. Their tastes in music probably consist of good things, real music. I listen to a large variety of music, and out of all of it, Vocaloid is, I think, the least likely to be "real music". I actually am more against the Vocaloid fans. Not all of them are like this, but many of them can't accept it if someone dislikes or hates Vocaloid. And they constantly go out of their way to insult and harass those people. Overall, I don't care about the Vocaloids; just the music that they are used in.