I'm not much into the idea of tours, but my wife is and all in all it seemed like taking a tour would be a better way to see the island than driving around, especially for me who would be tunnel-visioned and clenching the wheel of a rental car around the steep switchbacks, and perhaps getting lost along the way.
We did both of the full-day tours UTC offered, on back-to-back days, saw all the major sites, stopping at multiple scenic overlooks along the way, and had a great time. Noora (tour guide) and Nuno (driver) were both great--informative and enjoyable to spend 16 hours with talking about all sort of things (mainly the island, of course, but plenty of other things).
The bus was comfortable and had great visibility. (This was one of UTC's small, ~12-16 person, busses, which was not filled on our tours. When the tour has more tourists they use a larger bus.)
The lunch meals, restaurants, and locations were excellent.
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