Porto - relax and wine
Porto has really nice city centre and when you get outside the main touristic zones, you can feel the Portugese atmosphere everywhere. It is possible to walk almost everywhere, maybe except for beach. But transportation costs are slightly higher than in Lisbon. I really appreciate the low or none entry fee for most of tourist attractions. If I ever go back to Portugal, I will come to Porto again.
Insider Tip:Take a time to visit Porto's beaches. Taste Francesinha and some pasteries, eg.g from Bolhao market. And don't forget to taste some wine from Porto, maybe in connection with visiting some of local wine cellars (e.g. Calém).