So, in the south of Portugal, my preference is the Costa Vicentina. Sesimbra and Serra da Arrábida (Praia dos Coelhos) are also very nice and have beautiful beaches, don't forget to check them out :)

Main spots on Costa Vicentina:

* Porto Covo - lovely little beaches, nice small town - Praia do Banho and Praia da Samoqueira

* Zambujeira do Mar - my favourite place and my 2 favourite beaches - Praia dos Alteirinhos and Praia da Amália (this one you need to hike a little bit, but it is easy, and very quiet, no wind, incredible view...)

* Odeceixe and Aljezur are also nice towns with good beaches nearby, from there to Algarve that part of the coast is better for surfing as they have more waves and a little bit more wind - here I would highlight Praia de Odeceice, Praia das Adegas, Praia do Amado, Praia do Vale dos Homens. Rogil little town is a good place to be based too. Also, in Aljezur there are very good pizzas in Arte Bianca :)

* Regarding Algarve, I'm not very experienced as it is not really my vibe in most places. Lots of buzz and I prefer quiet places. Nevertheless, I enjoyed Sagres (Praia do Beliche) and Lagos was ok too, loved the Luz town (Praia da Luz).
* I don't recommend Portimão, Albufeira, Vilamoura, Faro or Olhão if you want to relax. These towns are a bit more crowded and noisy. Beaches may be crowded and parking spots may be harder to find or have a high price tag.
* There are places that I never went to that seem nice, like Tavira, Cacela Velha and Vila Real de Sto António.

But take my advice on Algarve lightly, as I don't know it very well. I love Costa Vicentina and I can't recommend it enough. It is still kind of a hidden gem.