Porto is a shitty city, everytime I go there I feel like I'm in Spain.
Lisbon has too much polution and ghetto corners full of gangstar people that need to be in groups to feel like they're strong when alone they get slapped and get unconscious everywhere.
Lagos is close to Olhão and it's nowhere near as beautiful nor nice. It's also one of the worst cities to live in according to some studies.
Coimbra is nice, but not as cool as Guimarães, but it's nice, a city with the same style, historic city with many students and people with good culture. Have loads of friends living there and they say it's pretty much like Guimarães, not as cool tho, but it's good for a change.