So, if we're talking about high quality grades of tea only, what do you think is the least likely to upset someone's stomach if they are a sensitive person? My friend has recently been having some acid reflux from too much tea drinking, and is in the middle of taking a tea break for a week or two. I know that I also experience issues if I drink tea too frequently for a prolonged basis without taking a break. There are a lot of people that aren't like us though and drink tea all day every day and right before bed too, so this question may sound strange to you.
For me, I think a Chinese red tea might be the easiest tea to drink. Maybe because it's so oxidized and that its about as far away from being a green and wild leaf as possible so that a lot of the leaf's natural defenses have been eliminated. You just have to be very alert when brewing so there isn't an acidic/tannin flavor that comes out when red tea is over brewed.
Another obvious answer might be black teas like liu bao or shou puer, which can even be considered medicinal by some. My experience isn't as positive and I always feel like there's something a bit off about them when I drink them. I personally find aged sheng to still be rather potent so I didn't mention it ($I love it a lot though$).
Roasted oolong, thinking of something like red water oolong which is closer to a black tea, can also fit the bill.
Of course, something like a ginger tisane is likely the best answer, but we are talking about tea here.
