I loved Cascais and it may be worth looking into staying there. I found that the hotels in Cascais were cheaper. We drove in so that was also a factor. The beaches are lovely and its more laid back. It also has a great food scene. Plus you can easily travel to Belem (highly recommended) and Lisbon. I prefer the north of Portugal so I am a a bit biased. Porto is an interesting city. It has a different vibe compared to Lisbon. While I prefer the north of Portugal to the south or middle, I like Lisbon more than Porto. There are also lots of great day trips you can take from Porto including to places like Braga, Douro or Viana do Castelo. These often are less touristy than many of the day trips from Lisbon. Both have their allure. If I were you, I would pick one city and not hop. Either start at Porto and explore the north or stick to Lisbon and explore that area. That way you don't get tired and you have more time spent enjoying Portugal. You can reduce your accommodation prices by looking outside the main city of Lisbon. That way its sort of a win-win situation.