Oops forgot to mention monk fruit which appears safe as well, both are from natural sources. Monk fruit is much more expensive however. I saw one study that suggested stevia might have anticancer properties, although that might have been the whole leaf which includes a bitter fraction that is removed from store bought stevia.
I think that “bitterness” might be one of those genetic taste bud type things, kind of like some people dont know that cilantro tastes like lemon Pledge on an anus. When I eat stevia leaves there is a tiny taste maybe like a glass of weak tea. Some people just seem to get hysterical about the bitterness but I cant find it.