I'm not that well-versed in such terms, but from what I know, mericlones and keikis are generally the same thing, plants that are genetically identical to the parents. However, mericlones are created from meristematic tissue taken from the parent in laboratories, while keikis are produced naturally by the parent. You can learn more from the explanation here
http://www.orchidboard.com/community...does-mean.html
For me, I think the main drawback for mericlones against keikis, is the price. (Keikis are cheaper without all the lab work and such)