There's no 'best' team; nearly any Pokemon will do fine as long as you train them enough
In terms of typing though, first uses Psychic (Dark type moves help in particularly - stuff with Crunch for instance. although Electric takes out the first three). A Psychic type does well against Koga's team for the most part, as does Fire. Third is fighting (Flying/Psychic mostly), fourth is half dark types and poison types and last Electric works well, as does Ice greatly against over half the team. You can check the teams for more details with a quick google search.
If you have any other questions please use the Help thread sticky at the top of the section next time. Closed.