There is no massive difference between the Vocaloid. The most important thing is whether the producer is skillful enough as to use them to make a good sound.
But the best vocaloids are probably the new Append ones. There are also a few songs which makes some of the vocaloids sound realistic.
Other then that, tune wize, they should more or less be perfect.
No, Akiakane is a Nico Nico Singer; not a Vocaloid.
No, Hatsune Miku is not an anime. Hatsune Miku is a vocaliod. A vocaliod is a computer generated singer, but Hatsune Miku is by FAR the most popular in Japan.
Len!
Japanese singer Gackt.
From the internet (I don't suggest this) or buy it in Japan
The original singer for the Servant of Evil is Kagamine Len with Kagamine Rin providing backup vocals.
Vocaloid is not an anime because, well, vocaloid is a program made in Japan where you buy the characters and the sets and you can make your own videos. Sometimes they're fan-made and other times they're made by the actual people. So, to answer your question, Vocaloid is a program, not an anime or manga. Vocaloid isn't an anime, but they have made a manga of it. It's called Hatsune Mix, and you can read it on onemanga.com.
In Japan. It cost a lot of yen, though. Or you can get it on ebay, amazon or somewhere.
She is a utaite (Singer) from Nico Nico Douga, and she impersonates Kagamine Len (Vocaloid). She is well-known for her lower range of vocals and sometimes said to be one of the best Len impersonators.
Yes, Ai is a vocaloid. A vocaloid 3 to be exact.
Vocaloid fans like Vocaloid. Vocaloid fans are located around the world. Vocaloid fans also have a tendency to like Japanese animation (anime) and comics (manga).
Piko is the name of both the Vocaloid and the voice provider, who is naturally not a Vocaloid.