Staying in Lisbon

I don't think it is too many days, particularly if you are going to day trip to Sintra and other areas. My only thought is that if you are driving up to Porto you might be cutting it a bit short. 2 nights there only gives you one full day. You can also take the train to Porto.

Consider carefully if you want to spend the money for a rental car for one day. I assume you are considering stopping in a couple places on the way. A 1-day rental is usually expensive and there may be a big drop-off fee. You'll probably want to add a toll reader to the rental. And you don't want to drive in Porto, so the best thing would be to drop the car at the airport and take the metro into Porto. If you are planning to use a car after Porto to other places in Portugal, you're probably better off taking the train from Lisbon and renting a car when you leave Porto. You will not want to drive in the city!

While I could find enough to see and do in 5 full days in Lisbon, I would be hard pressed to choose what to skip in Porto with only one day there.

I would cut Lisbon to five nights, and add one night to Porto. Five nights give you three full days for Lisbon and one for Sintra, which lets you enjoy Lisbon at a not-too-quick pace.

I agree with the other posters. Two nights in Porto isn’t worth the time and energy to get there. You need at least two full days - three nights - to make it worth your time.

And, I would not drive. The train is so much easier and cheaper. You could even stop in Coimbra for a few hours (if you can find someplace to stash your luggage - which has been a challenge in the past).

Kathryn, we were able to drop luggage at the TI in Coimbra a couple of years ago. I can't remember if we could lock it up. I think not and we just took valuables with us. Right by the main square.