I don't think it is easy or even possible to make a list of artificial sweeteners in order of how dangerous they are. Over the years, each one of them has been accused of being carcinogenic, mutagenic or otherwise dangerous. Cyclamate used to be one of the worst offenders, but the latest new suggest that cylcamate is at least not carcinogenic. I don't know who pays for what research and who can be trusted. I will however say that I stay away from all of those sweeteners when possible.
I have tried stevia out of curiosity, but it too has been badmouthed. Just because it's a naturally derived substance doesn't mean it's safe. I don't care for stevia's taste anyway, but do prefer plain old sugar, which I do not consume in vast quantities anyway.
Let's not forget that recommendations change over time. Often, what was supposed to harmful yesterday is just fine today, and vice versa.
In the end is comes to making sensible choices, which includes moderation. Unless one has a metabolic disorder like diabetes, one does not need to resort to using artificial sweetners (and fat-free foods, low-carb tit'ntat) as long as one eats appropriate amounts of proper food. Washing 5 donuts down with a liter soda just isn't natural, even if it's all diet and fat-free.