18 days in Sept, rental car options...

I would keep the car for Sinatra as you can include Cascais and the route through old cork forests between the two.
I haven't seen further south, but Rick often misses plenty of stuff as he tries to limit to what HE considers to be top locals...that can be fitted into an American vacation allotment.

We spent about the same amount of time there, a little over a year ago, just before things shut down.

We also flew round trip to Lisbon (used miles, to do open jaw on Delta out of Porto was much more and required a connection in Europe).

We landed, spent a night in Lisbon, picked up the car, drove most of the time, returning the car about a week before flying home in Porto, doing Porto, then Train to Lisbon for a few days before flying out. For us, it was the same whether we returned at the same location, or returned in Porto.

With a car, we were able to hit a bunch of places, our thought was to sample a bit of everything, with the idea that on another trip we would focus on what we liked.

For Evora, we just made a long stop, including the megaliths outside of town, then drove on to Monsaraz, a little hill town for the night. We then headed south to the Algarve.

We stayed several nights in Loule, not on the coast, our reason was that they have a nice series of Parades for Mardi Gras (it was that time of year), so we used it as a base for the Algarve. We managed to spend time in Tavira, Lagos, and Salema, as well as stopping several other small places along the coast as day trips. You could just pick one town, or two, and day trip as well.

We also spent nights in Tomar, Coimbra, and Peso da Regua.

Can't help you with Sintra.

Other stuff: We had a phone with Data, using Uber was easy and dirt cheap at that time. Driving was easy, the expressways had very low levels of traffic and are fast, some of the small towns can get tight, and any parking garage come with inches to spare...a compact car is not a bad idea. Do get the toll pass from the rental agency, saved us money, even if it does not, it is worth the convenience, in the Algarve, we really did not see an option to manually pay anyway.

Edit: While the Rick Steves tours may not go South of Evora, the Rick Steves Portugal book does cover the Algarve.

Hoping to get over for this October.. so this is based only on research.

All I have read and been told strongly suggests NOT to have a car for Sintra. There are lots of posts with conversations why - mostly because of little parking and lots of one way streets. I understand there are lots of ways to get from the train station to the sites (way up hill).

Thought might be - Arrive in Lisbon, transfer to Porto - same day (train is @ a 4 hour trip - check Rome2Rio or you might check on a connecting flight that day), Porto, collect car as leave Porto, Douro Valley, Coimbra or Obidos or Tomar (anywhere mid-country), Evora, Algarve. Lisbon (drop car as arrive) I would save at least 4 nights .. could do Sintra as a day trip (might be able to arrange a day tour?). If you can squeeze a day from somewhere - maybe stay last night in Sintra. Then some sort of transfer to the airport on departure day (from Lis. or Sintra).

This is a lot of ground to cover in 2+ weeks - I think the reason many group tours leave off the Algarve is it's in the wrong direction from many of the "larger" sights. Depends on what you want to explore while you are there.

Someone suggested Julie Dawn Fox- Portugal (web/blog) for info and hints (I got lost down that rabbit hole- thrilled I did). She has great info (as does RS's guide). There are lots of you-tube walks and food tours - to give you an idea of what you will see and many want to do.

Have fun! If you get there - we should be able to follow!!!

Though I wouldn't rent a car to get to Sintra from Lisbon, and the upper part of the town is not car friendly, having a car allows for the trip to the coast and some add ons to the day. I did it with Cascais as a cruise port visit, so enjoyed the road trip aspect. If you chose to give that area an overnight, there is local bus transport to do similar.
You could most likely get a taxi from Sintra train station in the lower town to the upper historic sites, or walk it...but there is a fair amount of walking already so why not cut off some milage with a taxi. When suggesting a car, I would suggest similar for ease of parking. Park in lower town and walk or taxi up.

You don’t need a car in Lisbon or Porto. Due to traffic and parking issues, a car is problematic both places. Especially if you are spending extra on an automatic, I would wait until leaving Porto before picking it up. Arriving in Lisbon then taking the train to Porto makes the most sense.

I agree that a car in Sintra is also a headache. There is a tourist bus that will take you up to Pena Palace and taxis and Uber’s are cheap if you want to go out to Montserrat (highly recommended). Be aware there is way too much to see in Sintra for a day trip. But, with your time parameters, that is likely all I would do. I would recommend adding a day to Lisbon if you want to devote a day to Sintra.

Unless you have a real reason to visit the Algarve, you might want to skip it this time. In 18 days, it will be hard to do the rest of the country justice. If you have to have a beach visit, there are many nice beaches closer to Lisbon. Admittedly, they don’t have the spectacular rock formations of the Algarve, but are quite lovely.

I will second the recommendation of Julie Dawn Fox. She has excellent information and recommendations. I actually agree with her recommendations more than RS.

So happy to see you planning a trip to Portugal. The tourist industry really needs you!

With 18 days, I also wouldn’t try to cover the Algarve. If Portugal is open for travel, then the Algarve will be heaving with tourists. There is plenty to keep you busy further north, including some great beaches, if required.

I wouldn’t take a car to Sintra, as it’s busy and parking could be an issue. The train between Lisbon and Porto is the best option.

I stayed near Caldas da Rainha, which was a good base to see Obidos, Fatima, Alcobaca, Batalha and the coast. Nazare, as recommended by RS was a disappointment and I wouldn’t return there. (Salema on the Algarve has been ruined by overdevelopment and I wouldn’t bother visiting there these days - another RS recommendation). Caldas used to be the centre of the tile making industry and the external walls of many properties retain this feature plus there’s a good market there.

in 2018, we had a fabulous trip to Portugal as with 16 nights on the ground. Flew in to Lisbon, picked up a car on our way out of Lisbon and dropped it in Porto on arrival there. Flew home from Porto. With 2 extra days I would include Coimbra, which we skipped.
We felt we saw a lot more of the country with a car. The roads were excellent and well signed. Easy to get around. The people are amazingly warm and friendly, and twice when lost we had people take us by the arm and lead us to where we were going. Good value food and wine. Enjoy Portugal!

Lisbon-3 nts Day tripped to Sintra, picked up car on our way out. Drove the coastal route to
Lagos-4 nts Day tripped to Salema, Silves and Sagres. Stopped in Beja enroute to
Evora-2 nts Stopped in Tomar on enroute to:
Nazare-4 nts Day tripped to Obidos, Alcobaca and Conimbriga for the Roman Ruins. There is tons to see in this part of Portugal!
Porto-3 nts Dropped car on way into town.