If mango plant raised by seed there is problem of true to type, if the both races of mango have desired charecters from breeding point of view , which race we have to prefer.
From breeding point of view, mono embryonic race will certainly be better than polyembryonic since in the former race the embryo results from the combination of both male and female gametes. On the other hand, in polyembryonic, the embryos originated from female parent will usually predominate develop into seedlings while the one originated from zygotic embryo is less vigorous. Therefore, it will require some kind of molecular markers to validate the genetic identity of the seedlings.
If you will use both mono and polyembryonic races as parents, you may get away bu harvesting seeds from the monoembryonic one, i.e. use the polyembryonic race as male and monoembryonic as female parent, respectively. I hope these suggestions help your research. Good luck.