I would recommend either reading them in the publish order, or reading the Ender's series books first followed by the Shadow series. It doesn't hurt to occasionally switch books to be chronological either, but in general.., the published order is probably best. There are very few interactions between the two sets (Shadow and Ender), so the chronological order between sets doesn't really matter, beyond the first book of each (Ender's Game and Ender's Shadow)
