Aveiro, the called Portuguese Venezia is also beautiful. I don't want to say that algarve isn't beautiful but it's very touristic while in Central Portugal, around Porto, Aveiro, Espinho you can still find great places to buy, to live, to enjoy without feeling stressed by mass tourisum.
So many real estate properties to visit here, old, new, near the cost, near the Douro, the rio vouga....etc