I personally think a day trip is a bit too short for Samet. One of my favorite things there is having dinner on the beach, which takes place after the last ferry of the day. Samet's Ao Phai has the most nightlife; when I was last there things stayed pretty active until 1am. I wouldn't recommend Samet for a week's vacation unless you like things really relaxed, but it is fine for 2 or 3 days. For a day trip, Ko Larn or a hired boat to one of the small islands nearer Pattaya is probably preferable.