Warning: people are overpaying for airport transfers in Lisbon
I keep seeing folks book those fixed-price airport taxis for 40 euros... the metro is 2 euros and takes you right to the city center in 20 minutes. How many other cities have you saved money by just using public transit from the airport?
The metro in Lisbon is actually 1.65 euros now, but your point totally stands. @uma_nguyen24, Barcelona's train is a solid choice, though it can get super packed with luggage. My rule is to always check the airport's official transit site before landing.