This tour gives you a nice tour of the island and mountain views are worth the ride. A little too long for shopping but guess that is better than not enough!
We booked the island and shopping tour through Carnival and it turned out to be a a/c bus which was fine. We spent some time on the French side of the island with shopping there too. The shops right at the harbor are just as nice as anywhere on the island and offer all the duty free items you might want.