Adventura Mexicana is right around the block from us, spitting distance. We love to go there for breakfast, their divorced eggs are so good. It would be great if you are able to do both trips, but remember Playa is a great place and the beach is lovely. It is possible to do the ruins and then catch the collectivo back to Akumal for a swim in the afternoon. Good luck on the decision it is a difficult one if your time is so limited. Try to get to La Fragata for a meal while in Playa. It is a small place you may pass by not thinking about stopping. It is across the street from PG's on First Ave and 26th. Right around the corner from Mexicana.