Karites, Samaritans, and Rabbanites? Different Sects of Judaism?

I know the basic differences between them pertaining to the Torah, Tanach and Talmud, and I know that they all believe in the coming of the Jewish Messiah, but how do the criteria in determining the Messiah differ from the Rabbanites since the Karites and Samaritans do not believe in Maimonides 13 Principles? Which is the oldest branch of Judaism out of the three?