Traveling with 5 adults over two weeks -- rental car or train?

We traveled to Barcelona and the Basque country in 2019 and just last month to Andalucia. Both trips we rented a car and self-drove. Fabulous experience both times. You do not want to have a car in Barcelona but elsewhere, all good. Parking is readily available for a fee. Unlike Sicily, a larger car should not be a problem . Fyi, we enjoyed Barcelona but Montserrat was super crowded so we would not return there. The Basque country was wonderful! We also enjoyed Seville. The Alhambra is a must do but this September Granada was uncomfortably crowded. Happy travels!

Thank you, mml! Did you pick up the rental car in Barcelona? Which company did you use?

Yes, we picked up the car at Barcelona airport, travelled and then dropped it off before spending time in Barcelona. Am thinking it was Budget but don’t remember for sure.

You will need a minivan. We are a family of 4 and we’ve rented SUVs and estate cars. Last trip we had 6 people in a full size van. For 3 people in the back seat of any vehicle, it would be a squeeze. Then you have to consider luggage: at least 5 carry on bags and probably 5 backpacks, daybags (assuming you all pack light). That will not fit in an SUV. Vehicles are smaller in Europe.

The cities you mention are easily accessible by train. None of them are places you would want to drive in.

Take the train. You would have to deal with a large van (you would need it with 5 adults + luggage).

I always get a rental car, but for the places you’re going, there’s no need for one. A rental car is nice when you’re stopping at places not well served by public transportation. As you focus your itinerary, look at places you’d consider stopping to see if you had a rental car. That might help you make your decision. Parking in the big cities can be a pain with parking costing 20€ or 25€ a day. Another consideration should be the age of any parking garage. Those built before the 1980s were not built for large vehicles. I had an experience around 2004 where my small rental barely fit in a garage in Ourense, literally. There were only a couple inches on either side of car before there were the garage walls. Fortunately, the vehicle had a sun roof had we gotten stuck and needed to get out of the vehicle. If you do decide to rent a vehicle look for lodging that has its own parking. It will most likely be away from the historic center.

I rented through Costco, the rental company was Enterprise, my last couple trips to Spain and we rented at Madrid’s airport.

I feel that the roads in Spain are very well marked.

Since you’re starting to plan now and can buy heavily discounted tickets on the high-speed trains ( in theory Renfe train 🚂 tickets first go on sale online 90 days in advance). The high-speed trains will take you from Barcelona to Madrid, Granada and Seville. The tickets for Barcelona to Madrid cost as little as €19 if you buy them in advance when they first are for sale. www.TheTrainline.com will show you all the high-speed trains—IRYO, Renfe, Ouigo— You’ll also be able to cover those destinations in a fraction of the time a vehicle will take to drive the same distances making the itinerary a challenge to cover by car in only two weeks. There also is a morning Alvia train between Madrid and San Sebastián that takes 5 hours and can cost as little as $15.
The Basque Country could easily take a week by itself and might best be saved for another trip to Spain sometime in the future.

Some of the distances you'd cover are significant and would be nearly a whole day in a car vs 2-3 hours on the train. Parking is rarely difficult to find, but it's expensive. Add higher costs of tolls and gas, and the economy of a rental car starts to fade.

So True.
I just returned from 3 weeks that covered Barcelona, the Costa Brava, Madrid and the Basque Country where we had a car.
The trains were fast and fun. And you can relax as a passenger, walk to the cafe car for a coffee and take some photos of the castles and towns from the train windows.
The car rental got us around in the countryside and is necessary to make the best use of time to see more of the rural towns and villages. The complicated and inconsistent signs on the Spanish highways were a real challenge, as were the roundabouts that unexpectedly appeared on highways.

We’ve needed two separate trips to include destinations you mention - one north, and one south. Our north trip started in Madrid, then with a 5 hour train ride to Bilbao, then a rented car to eventually work our way thru parts of Basque Country and on to Barcelona, where we turned in the car before our stay in the city. If you did that in reverse, rent a car/van/SUV when you’re finished with Barcelona, work your way to Bilbao, turn in the car and enjoy Bilbao before riding a train to Madrid.

Alternatively, maybe go as far into Basque Country as you want, turn back to Barcelona to return the car (no one-way drop fee for picking up and dropping off at separate places), then take a cheap flight (maybe on Vueling?) to, say Granada. Rent a car to reach Seville, or use a train. Same for reaching Madrid at the end … maybe train, maybe car. Our “southern Spain” trip was a mix of train and rental car.

In May from Barcelona we flew Vueling Airlines to Granada. Airfare was cheap and on time. In Granada we picked up a car from Enterprise. I studied locations and got the car at a city location that was one block from a gas station and highway on-ramp. The drive was easy and pleasant to the White Hill Towns (Ronda, Arcos &Jeriz). Driving distances were not long between those distances.. We then drove to Seville dropping the car off at the main train station which was easy. After touring Seville we took a high- speed train to Madrid. Note that there are two different train companies for that route. It is pretty easy to get to most of those locations with air and trains. A car is only necessary for going to smaller villages.

Forgot to mention that I rented through Priceline. It was the cheapest. I would periodically look at the prices and rebook when I discovered the prices went down even more.

Thank you to all of you who weighed in with sage advice -- all very helpful/constructive! Your experiences will certainly make our trip easier to plan.