Portugal itinerary advice

Yes, without a car, it is easy to link Lisbon, Coimbra, Porto by train. It is also easy to visit Tomar if you want with a direct regional train from Lisbon, and one connection (Entroncamento) from Tomar to Porto.

I liked staying in Tomar as a base with a car. When you say, add a night or two, do you mean taking time from somewhere else or extending your time in Portugal? If you mean more nights in Portugal - the more you can add the better, you won't regret it.

A logistics note - the main train stations, Coimbra-B and Porto-Campanha, are outside the historic centers. You can wait for a local train to take you into town, but you will save time and hassles by taking taxis to/from your hotels. Taxis are reliable and not expensive. There are two types of fast trains, IC and AP. The AP trains are a little faster and definitely more comfortable. Check schedules and prices here. You'll save money if you buy in advance.

To add to the above, taxis and uber are very cheap in Portugal. For short city trips with two people, fares rarely exceed five euros.

I meant add more nights, not take away from other places, yes. No problem with taxis and Ubers, I don’t hesitate to use them!

Any ideas on places to stay in Coimbra? Better to stay in the Baixa or old town?

If you add nights, there's no limit to great places. You could overnight in Evora and have time to visit a cork factory and tour some megaliths. Spend a couple nights in Tomar - the gothic monasteries at Alcobaca and Batalha are beautiful and quite different from each other. I quite liked the day/night I spent in Aveiro. Those are just places I chose from among many.

We loved Porto, especially the B&B there (The In Patio Guesthouse).

You should spend some time in the Douro River Valley. You can take the train down the north side of the river. Need more than one day for that.

We did a great day trip to Santiago de Compostela in NW Spain that was great.

There are a lot of sites that interested us in Lisbon, so I would do only one day trip from Lisbon. I think Sintra or Cascais makes the most sense since they are closer than Evora. We spent 5 nights in Lisbon, including a day trip to Sintra, and we didn't see everything we wanted to see in Lisbon. We didn't have time for the Tile Museum, and I would have enjoyed more time just for wandering around this very interesting city.

If you add a couple of days, I would encourage to see Evora and spend a night or two. There is a lot to see there, good restaurants. And a number of well priced hotels.

If you were to choose between sleeping in Coimbra or Evora, which would you rate higher?

I stayed overnight in both. It's hard to choose. I really enjoyed the fado performance in Coimbra that's near the end of the RS city walk. If you do that, you'll probably want to stay overnight there. I had dinner at the restaurant a few meters up the stairs from the fado. I think it's also described in the RS walk.