I live in the deep south where sweet tea is de rigueur. I serve only unsweetened tea, but offer a small pitcher of simple syrup (1 part sugar per 2 parts water). This lets everyone who wants sugar sweeten to taste.
I keep the syrup in the fridge, and also use it for hummingbird feeders by diluting it with an equal part of water. When my BIL found out about this he claimed he felt a little fluttery after drinking the tea.