Ribeira and the Baixa (Aliados, Rua das Flores, Clérigos, São Bento) are the walk-everywhere core and the first-visit base, holding The One Monumental Palace, Casa da Companhia and 1872 River House. River-facing rooms in Ribeira are the most atmospheric and the noisiest, and none has a car park. Cedofeita and Miragaia to the west are quieter and residential, river still in view, and Torel Avantgarde holds the Miragaia hillside. Foz do Douro is a calmer Atlantic seafront fifteen minutes away by taxi or forty on the Line 1 tram, and Vila Foz is there. Vila Nova de Gaia, across the Dom Luís bridge, has the port lodges and the best view of Porto itself, with The Yeatman on the hill and The Rebello on the water. The Douro valley is a different holiday: 97 minutes to Pinhão by car on the A4, or about 2h20 on the Linha do Douro from Campanhã, and that is where Six Senses, Quinta Nova and The Vintage House are.
The airport is 11 to 15 km north: 20 to 30 minutes by taxi or Uber for 25 to 35 euros, or about 27 minutes on Metro line E to Trindade for 2.30 euros on an Andante card, which costs 60 cents. Line E runs from six in the morning until one at night, and a 24-hour Andante for the central zones is 5.35 euros. You do not need a car in Porto and you will regret parking one. You do want one in the Douro, or a driver, because the quintas are strung along narrow valley roads and the train only serves the river line.
May to early October is the dry, warm window and the peak, though warm here means low twenties rather than thirties, and the Atlantic tops out near 19 degrees in August, so Foz is a seafront rather than a swimming beach. São João on 23 to 24 June is the loudest night in Ribeira and Gaia, and worth planning around either way. The Douro harvest from mid-September to early October is the valley's most expensive fortnight and its best one. November to February is mild, wet and cheaper.
Three nights in Porto and two in the Douro is the shape that works. Three days does the city without racing it: the Baixa and Ribeira on foot, the port lodges across the bridge, then Foz and Serralves or the Casa da Música. Then move up the valley rather than day-tripping to it: the drive back after dark is the worst part of a day trip, and the Douro is at its best at breakfast and at dusk.
The honest part. Porto is steep, and Ribeira to Aliados is a climb whichever street you take. Ribeira and the Cais de Gaia are crowded from lunch to midnight and noisy on the water side, so ask about room position first. The city has grown into its popularity faster than its pavements have. December is the wettest month, about 195 mm over thirteen days, and October to May is properly wet rather than drizzly. And the Douro is several degrees hotter than the coast in high summer, which is welcome in May and punishing in August on a terrace with no shade.