>>27578574RBY or RS because on those games the pokemon that appear are the ones in their Pokédex (150 in RBY, 200 in RS), though you must either use a save modifier or VBA-Link for emu; or have both games in their console to have all Trade Evos and Version Exclusive.
I don't recommend you: GSC due to depending on RBY games to get Kanto starters, Kanto Legendaries, and Fossilmons.with exception of Aerodactyl; E due to it gives you a National Dex that you can't finish due to most Pokemon must be traded from FR/LG.