I have been using some flavored teas, like Lipton has a mangosteen and white peach green tea. It's great just by fermenting the kombucha. I usually use at least 2 black tea bags along with the green tea.
But I also did a batch of that, then put fresh strawberries and peaches in it, and it was good. Strawberry is strong.
Lately, the best flavor is any kind of tea for the kombucha, then I add this Superfruit 7 juice from Aldi. I'm sure there is another "real" brand of it. I put 1 oz of juice in a 12 oz bottle and fill it with booch. Leave it out on the counter for 3 days, then in the fridge. It got really fizzy after about 2 weeks cold.
I also was fermenting it all the way out, then making a batch of Yogi blueberry green tea with sugar. Mix it half and half booch to fresh tea, or 75/25, depending on how sweet or tangy you want it. That was pretty good, too.
I like to change it up and try different flavors. I saw a spiced cider recipe - heat the cider with spices, then add it to the booch. I might try that with some, although aren't we getting pumpkin and cider spiced out?