Ordinarily I prefer Campari with grapefruit juice and/or soda, but context counts:

Negroni

1 oz gin
1 oz Campari
1 oz sweet vermouth
splash of soda (optional)

Serve over ice in a lowball glass garnished with an orange slice and a twist of lemon. Preferably enjoyed in the lounge of a grand hotel in Nice, accompanied by hors d'oeuvres and the reminiscences of a venerable lady with an interesting past...