We stayed at both resorts a couple of years ago, and loved each. They are not far enough apart to make a huge difference, but our overall favorite was Playa Andaluza, probably influenced by the oceanfront 3 bedroom we had there, compared to the oceanview 2 bedroom at Marbella. We also had really great experiences with the staff at Playa Andaluza, and just OK at Marbella. In January you probably won't be using the beach or outdoor pools much, but we liked the beach better at Playa, and the view from the restaurant better at Marbella. Although there are lots of restaurants nearby, I think Marbella had more within really close walking distance.
Gibraltar is really easy to do on your own. Just park the car on the Spanish side and walk across the runway or take the bus into town. We loved Ronda in April, and it should be less crowded in January. There are many closer, less tourist oriented, white villages as well, but Ronda is one of the most spectacular. The Marriott trip to Morocco was cancelled due to wind, and since I had already been to Morocco and my husband did not have a day trip on his must do list, we didn't try again.
Driving is only difficult if you are not used to driving stick shift on hills. Also, getting used to entering the main highway along the coast from a dead stop, since there are stop signs at each entrance. The smallest car you can manage comes in handy on the very narrow streets in many of the villages. Even with a small car for just the two of us, we had to fold in the mirrors in places in several towns. However, on the long uphill grade up to Ronda, we paid the price with not enough power to stay out of the truck/slow lane. In Ronda, not a problem, but in Arcos de la Frontera and several others, we were happy for the small car.
Have fun! We are going back to Playa this April, and if I can pick up another week at Marbella or Son Antem, we'll enjoy another week again there as well.
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