Awesome that you’ll be back for a 3rd time, watch out…that’s how it starts 🙂
Manuel Antonio is a great place to visit if you won’t be renting a car. You can easily get around on the local bus, which runs about every half-hour, or by taxis. If you book tours like rafting, canyoning, etc. they also usually include transportation from your hotel. As for suggestions on places to stay, you can check out our post, Manuel Antonio Trip Planning for some ideas but definitely try to find somewhere either on the beach or along the main road so you can get around easily. For other activities, there is Manuel Antonio National Park, which is great for wildlife viewing and zip-lining/canopy tours are also really good in the area. If you want to get out on the water, a catamaran/snorkel tour is always nice or a tour of the Isla Damas mangroves to see more wildlife. Hope this gives you some ideas, have a fantastic trip!