Portugal south

We prefer the Portugal north and west of Lisbon. The Douro Valley is amazing.

The international drop-off fee will almost certainly be enormous if you rent in Portugal and drop off in Spain.

There is some bus service across the border. You'll probably have to transfer at least once (perhaps in Faro).

You can pick up a Spanish train in Huelva; I don't know whether the trains run any closer to the border than that. I think that would be the best way to get to Cordoba; you'd be traveling through Seville. You'll be able save a lot of money on the train trip if you buy early and snag a promo ticket, but it will be non-refundable and non-changeable. If you don't object to buses on principle you should compare the travel time and cost of an all-bus trip to a combination bus and train trip. The bus trip might be quite a bit cheaper. I think the trip to Faro will require a rede-expressos bus, then the Faro-Seville-Cordoba journey will be on ALSA.

Traveling from the Algarve to Estepona may also require you to travel via Seville. It's likely to take considerably longer to get to Estepona than to Cordoba. You can explore your options on the website Rome2Rio.com, but do not trust the fares, travel times or frequencies it displays. Just keep clicking through until you find a link to the transportation company's website and check fares and schedules there.

I have never been to Estepona, but I can't imagine that it has as much to offer as Cordoba.

Southern Portugal (the Algarve) comprises a series of mostly purpose-built modern resorts or smaller, older settlements that have changed character and been swamped by new development over the past 30 years.

Any coastal resort in Portugal or Spain will be very busy in July, so book your accommodation ASAP.

Tavira on the Algarve retains the most character and is smaller than Lagos, however the beach is out on the barrier island, which is reachable by a short 5 minute boat ride. There are buses from Faro and Tavira to Seville in Spain, which will be cheaper than paying a one way drop fee for car hire.

Estepona is a modern seaside resort, whereas Cordoba is an inland historical city, both very different in character. If you have spent time on the beach in Portugal, then Cordoba would be a contrast if you like history.

Estepona is a modern seaside resort

Jennifer, there's been a settlement at Estepona since the Prehistoric times! The Battle of Estepona took place in the 1300's, it's been in Moorish hands before being taken back by the Christians. The old town certainly couldn't be considered modern and although there has been some modern development it's not on a scale as much of the rest of the Costa Del Sol.

That being said, it's no Cordoba.

*Edit
Besides, wasn't this trip supposed to take place June 2019?

The original post in this thread says July 2020.

This trip is for July 2020.

Sorry, I stand corrected! I looked into Estepona a few years ago, looked on Google map and only saw a modern resort. I met someone recently who usually have 2 weeks there in September, but they say it is now very expensive and they can get a month in Fuerteventura cheaper than 2 weeks in Estepona.