Easy way to Waiheke is by ferry and hop-on-hop-off bus, which is what I did. But there is easy car hire on the island, so if you want to go to wineries at your own pace, or see the large part of the island not covered by the bus route, hire a car or bicycle. The island is truly delightful. I was there on a cloudless, brilliant blue day and it was like paradise. I did the bus trip and ended up at Mudbrick Restaurant (which I'd pre-booked) and had the most delicious lunch, sitting out on the terrace looking over the vineyards to the water. Perfect.