I guess I am in the minority here because we really liked Malaga. We spent 2 nights there and would have enjoyed a 3rd night. Regardless of what you decide to do, Malaga is NOT a place only to fly into and out of. That is how Rick Steves treats Malaga in his guidebook but I beg to differ with him.
If you have not already done research, you should read up on Malaga to see what wonderful things there are to do there. In addition to Rick's book, I used Lonely Planet and Michelin Green Guide. Malaga's center is beautiful with marble streets, lovely architecture and lots of restaurants and stores. It's a pedestrianized zone. For sightseeing you have the Cathedral and tons of art museums, such as the Picasso Museum. The walk to the top of the Alcazaba (Moorish fortress on a hilltop) is stunning with lush greenery, exotic flowers, towers, pathways, gateways, Roman Columns, arches, and a small Nasrid palace at the top. And the views! Stunning views of the city, the port and the Mediterranean. If you have the energy, you can also walk to the top of the Castillo de Gibralfaro.
And talk a walk along the seaside promenade and have drinks watching the sunset over the Mediterranean. And then there is the Atarazanas Market, a huge market with tons of stalls selling fruit, veggies, fresh fish, etc.
And you have some lovely coastal ambiance instead of being inland all the time. I think Malaga is very under-rated. Looks like you have 5 nights in Granada. You certainly have time for a day trip to Malaga. It's only about 1.5 hours by ALSA bus.