In a 1 1/2- to 2-quart glass measure or bowl, combine basil leaves (see notes) and sugar. With a wooden spoon, crush leaves with sugar until thoroughly bruised. Add water and lemon juice. Stir until sugar is dissolved, 1 to 2 minutes. Taste and add more sugar if desired. Pour through a fine strainer into ice-filled glasses. Garnish with sprigs of fresh basil.
All basils add fragrance to lemonade, but colored and scented varieties contribute extra personality. Dark purple basils tint the lemonade a pretty pink but have a milder flavor than green varieties. Lemon basil adds a lemon-drop essence. Cinnamon and Thai basils contribute spicy overtones. You can make the lemonade up to 1 day ahead; cover and chill.