Selfish as it sounds, when it comes to travel we prefer not to share. This year, new exclusive-use properties ensured we didn’t have to. In Tanzania, the 20-acre Thanda Island reserves all of its luxuries for just one group at a time. A party of up to 26 guests has the run of the isle’s gabled villa and bungalows, mahogany speedboat, white-sand beaches, and glass-rimmed pool. There’s no waiting for a table at the restaurant, no nudging for prime views of the local hawksbill turtles, and no rushing to get a seat at the beach bar—unless you’re running late for the sunset cocktail hour ($10,000).