My impression from these forums is that there isn’t a single artificial sweetener that doesn’t cause someone’s insulin to spike (insulin, mind you, not glucose; it’s insulin we really care about). The good news, however, is that most people, as far as I can tell, don’t react the same way to all artificial sweeteners. It seems to be completely individual, and you won’t know if stevia, say, is safe for you until you try it.
As @juice says, “natural” is a very iffy word. Yes, stevia is a plant extract, but then again, so is aspartame (discovered in asparagus, but found in many other plants, as well). And monosodium glutamate is found naturally in tomatoes and other plants in the nightshade family, but a lot of people don’t like how they react to it when it’s added to food. Gluten and lactose are other perfectly natural substances that people have problems with; not to mention the fact that apple seeds, peach pits, and potato eyes contain Prussic acid (also known as hydrogen cyanide). So being “natural” is no guarantee of anything.