Isla Perro is one of the biggest islands and one of the most popular ones in San Blas archipelago. This island is a great place for snorkeling and exploring the nearby shipwreck that is full of colorful fish and corals but there are a lot of bigger and smaller islands in San Blas so you can stay on any of them and it will be an amazing experience. If you are staying on another island you can take a boat day trip to Isla Perro and some other places, I was on a day trip from Isla Franklin and it cost 15$ per person.