What cities are you going to? If you're just going from madrid to san sebastian, it is much easier by train. But, if you love road tripping and want to drive along the basque coast, go across the border to france, travel up into the pyrenees and so forth, a car makes sense.

We did a combination of trains and car when we were there. Trains between the big cities and then we rented a car for the week we spent driving around the southern part of the country. But we are also a family of 4 so logistically having the rental car made more sense and gave us more flexibility.

We had no problems driving in Spain. We don’t like timetables though and like to go off the beaten path when we feel like it.

The trains and public transport are great for the cities. Driving is fine, but I would only bother with a car if you want to see a lot of rural areas.

I think it depends if you want to explore just major cities or smaller towns? For just a few days, seems like you don't need one and might spend most of your time in the city?

We were just there and did rent and the process was easy and for my DH the driving fine. (I hate driving anywhere including DC.)

Will be there over the holidays. Will only be there a few days. Deciding if we stick to trains to get to different cities or if it is worth renting a car. Will be in the Madrid and north area.