If I have 2 days to "spare" or extra should I try to see Azore islands? And if so is it better (cheaper) from Lisbon or Porto
From Porto you can do some really nice day trips too. Take the train in to Regua in the Douro Valley for instance. That is a fantastic place with lot's of natural beauty surrounding town. Or take the train up to Guimaraes which is the cradle of Portuguese history.
The Azores is a 3 hour flight from Portugal mainland. In my opinion you need more than 2 days to make that worthwhile. You have several flights to the island every day if you want to go.And they fly from both Lisbon and Porto. You will most likely get the best deal from Lisbon as you have a lot more flights from there.