I was lucky with my stevia. The brand name of stevia that I use is KAL, in the white powder form and I love it. I also tried some of the powdered stevia leaf, which is green and it tastes awful.
I was sick as a dog for years, when I was drinking diet coke which contains aspartame. I also drank no water, only 6 or more diet cokes every day. Along with a few cups of coffee, which of course I added Equal to. I will never use Aspartame again. I cannot believe they even allow it on the market......well, yes I can believe it. It is all about $$$$$.