Once upon a time, the most a gin-and-tonic lover could hope for in terms of a superior mixer was Schweppes tonic from the bottle, a merely decent alternative to the mouth-furringly sweet Canada Dry or subpar gun tonic. A new breed of high-end, all-natural tonic waters claim those days are over. Created to complement designer gins, the fizzy mixers shun low-integrity ingredients like corn syrup and synthetic quinine with the aim of elevating the overall G&T experience. The brands—Fever-Tree, Q Tonic and Stirrings—use more pristine sweeteners and genuine bitter quinine, an extract from the bark of the cinchona tree that’s said to cure malaria, fevers and cramps. We put the supertonics to the test at London Bar at the London NYC Hotel with three popular gins, each with distinct qualities: Beefeater (bright and citrusy), Plymouth (lean and peppery) and Tanqueray (bold and piney). Our panel included these gin-and-tonic savants: David Wondrich, a cocktail historian; true Brit and Tea & Sympathy owner Nicky Perry; and manager of the London Bar (and U.K. native) Duncan Halden.