Emerald, Platnium, HGSS, and BW/BW2 are pretty universally considered to be the best pokemon games, so i'd play those. Emerald hasn't ageed quite as well as the others due to worse visuals and a lack of a physical special split for typings/moves (In gens 1-3, all attacks of a typing either use your special attack or attack stat, vs after then when it's on a per move basis, IE fire punch, despite being fire, will be physicla attack based since it's a punching move), which adds a lot more strategy and pokemon viability.
Gen 6 is pretty shat on for it's causlaization and dropping of features from gen 4 and 5 but they are so polished and have so many quality of life improvements I still recommend them as well, though ORAS is pretty much trading emerald's extra content for more polish/quality of life stuff/3d models. Since they are somewhat casualized they might be a better restart point as well.
