In my opinion, Espanola has the most to offer in the main central islands.  Gardner Bay and Punta Suarez are a 1-2 combination of ocean and land animals.

Gardner Bay: Has a huge sea lion colony that lounge around on the beach and in the ocean.  We snorkeled near big rocks in center and a rock wall on the left side of beach.  Near the big rocks, I played with 2 sea lions and saw a white-tip reef shark (tintorera).  In the rocks near the rock wall, I followed a huge sea turtle for about 10-15  minutes and scratched its back / patted its head while it was feeding on seaweed in about 2 feet of water.  It wasn´t really thrilled with my head stroking.  In the sand, there was a whole area of rays of up to 4 feet across hidden in the sand.

Punta Suarez is an easy hike (2 hours done slowly) where we saw reddish marine iguanas (taking their color from the type of seaweed and algae they eat) which were fighting head to head, fearless Galapagos hawks near the pier, and surprise(!), another colony of sea lions. I realize I am getting a bit spoiled with natural lief.  There was a little sea lion only 3-4 days old.  We also saw:

- Blue footed boobies´ nests

- Masked boobies´ nests on the cliff

- Juvenile albatrosses (very ugly when they´re losing their feathers) and a couple of huge adults

- Fearless mockingbirds were everywhere.  Being that there are no natural predators in the Galapagos, animals are fearless.

- Tropic birds near the blow hole

- Beautiful panoramic view of cliffs and the ocean

- Cool lava lizards