Quick answer
What is the best photography route in Porto?
The strongest photography route starts in the historic centre, around São Bento, Aliados, Clérigos and Rua das Flores, then moves towards Sé, Ribeira, Luís I Bridge, Gaia and Jardim do Morro.
If you want details, focus on tiles, doors, balconies, churches and old façades. If you want dramatic views, go higher: Sé, Clérigos, Serra do Pilar, Jardim do Morro and Palácio de Cristal. If you want softer light, follow the river towards Foz or Gaia near sunset.
Porto rewards people who move slowly and look twice.