Driving Santander to Malaga

I’ve driven north and south through Madrid A1>A4 several times. I’d say that route is fairly straightforward but can be extremely busy depending on time you hit it. We’ve had clearish  runs and also stop/start. Avoiding the lunchtime rush a good idea.

Cannot think of an alternative route that doesn’t involve extra miles/time, maybe others can?

We much prefer the Salamanca route may be a few mile extra but no bottle neck no tolls just more relaxing . We hate the Madrid route.

Also if you have time to spare it’s good to have a couple of days in Salamanca beautiful city and lovely hotels

Last year I drove via Salamanca (which is a great place) to Santander and later returned via Madrid. I enjoyed the Salamanca route more, but the route from Santander to Madrid is nice (no tolls) and I don't think Madrid is very difficult - you don't go through the centre after all. First part of route from Madrid south is a bit tedious but very beautiful once you hit Jaen. Don't think there are any tolls. Enjoy!

I did this twice last year, stick to the motorways and dual carriageways, no need to go on the toll roads. The roads are extremely good, way better than the UK. You don’t go through Madrid, the dual carriageways bypass Madrid, like most major cities. Google maps will provide you the route with or without toll roads. 

Thanks for all your info on this post, I'm sure they will make an  informed descision based on all your input.