Avoiding crowds in Porto means keeping an eye on regular European travel patterns. It will be relatively busy in summer but quieter in spring and autumn. If you want to avoid the biggest crowds, the best time to travel is probably anything else than July or August. It is also a good idea to keep an eye on football. With FC Porto doing quite well in recent years, a big Champions League game can make the city super busy outside peak season. Unlike Lisbon, the city attracts only a limited number of cruise ships.