We were in Zante in September and did both the smugglers cove and turtle trip with Captain Spiros. We found both trips to be excellent - my partner preferred the morning trip to the shipwreck whilst I preferred the afternoon trip to the turtles. There is more swiming in the afternoon trip with the swimming from the boat in the cave being a highlight. How he got the boat into the cave god only knows. We got to see turtles and on the morning trip dolphins - as soon as he saw them Capt Spiros went out of his way to make sure we go to see them.
Margaris was reccomended to us by a local. We booked a car for 4 days for about 130 Euros which was way cheaper than our holiday rep had offered. And of course she said that the local companies were no good. What a load of rubbish! Glad we didn't believe her as Margaris were excellent - everything booked very simply with car delivered to our hotel. Car was small but that is just what you need on this island as the roads are narrow. I've driven a lot in Greece and the roads on Zante were actually very good - gets a little tight through the villages but once you are out of them it is fine. Car was a god send as the scenery is lovely and it allowed us to visit some very nice out of the way beaches. We also got to the outlook over the shipwreck before all the coaches turned up.