I've cycled the whole coastline. It's all good, from the Pyrenees foothills in the north to the more touristy Algarve coast in the south. Much less populated than Spain. However, the Portuguese seem to LOVE cobblestones, not only in towns but for whole stretches of roads inbetween - so I'd recommend 32mm tires or wider. The amount of work put into laying cobblestones is mind boggling, but I swore that if I caught up to the guy laying them (following in his father's, grandfather's, great grandfather's etc steps) I would seek retribution!!!
The Pyrenees foothills are nowhere near Portugal. Also, I honestly don't recall encountering much cobblestone. We did not ride anywhere south of Lisbon, in case that's where you found lots of cobblestone.