You should go to both Lisbon and Porto, as each city offers its own unique claim to fame. In Lisbon you’ll find a fast-paced city break, whereas in Porto you’ll find more slow-paced sightseeing. Both Lisbon and Porto have important cathedrals and historic buildings, but Lisbon has significantly more museums, monuments, and historically significant Lisbon neighborhoods. Porto is a nice change of pace from Lisbon, where you can take a break from the city life and enjoy sipping Port wine.