Just personal preference. Drinking black tea on an empty stomach sometimes makes me nauseous in a way plain coffee or other teas don’t, I’m not sure why (it’s not the caffeine since obviously coffee has more).
Green Tea is a greater source of antioxidants, but I drink three or four types of tea for variety sake, along with black coffee and water with and without lemon. Hibiscus tea has a slightly sour taste and I find Chamomile relaxing at night. But for IF purposes and avoiding insulin response, any plain tea will do. Good luck!
Black tea while fasting makes me nauseous. I can drink black coffee and other teas while fasting with no issues. No foods make me nauseous. There is something about black tea on an empty stomach that my body just rejects.