Health Benefits and Risks
Artificial sweeteners were first invented so that people could have sweets without the calories. They are sweeter than natural sweeteners, so we can use less of them.
However, studies have shown that people who use artificial sweeteners don’t necessarily have better health outcomes. The problem with an artificial sweetener, is that when you eat something sweet, your brain is triggered to be ready for calories. Your brain is then more likely to tell you, ‘Hey, we need more calories, keep eating!’, which will cause you to over eat. [1a,b, C&EN]
According to the National Health Institute (NIH), there is not enough evidence to show whether or not artificial sweeteners help people lose weight and reduce risk of disease, or whether there are definite safety risks. Yet, they are still approved by the FDA. [3a,b]
Bottom line – stay away from artificial sweeteners. Take a close look at the processed foods and drinks you’re consuming that are labeled as ‘sugar free.’
In my personal opinion, most of the sweeteners recognized as ‘natural’ are all relatively the same in terms of health risks. They can all contribute to changes in blood sugar, insulin resistance, and other diseases. Practice moderation.
Watch out for sweeteners high in fructose. Remember – excess fructose goes directly to the liver to produce fat.
Here are a few examples for reference:
- Maple syrup – 30% fructose
- Honey – 40% fructose
- Sucrose – 50% fructose
- Agave – 70-90% fructose
I found a quote from Robert Lustig at UC San Francisco in C&EN Magazine, who thinks sugar should be removed from the FDA’s ‘generally recognized as safe’ list. I think it’s an interesting opinion. 
Sugar has gone from being a condiment to a dietary staple, Lustig says, and he thinks it should be controlled like a narcotic. “If a substance is abused and addictive and it contributes to societal problems, that’s criteria for regulation.”
Sugar alcohols are regulated by the FDA, and can cause laxative/bloating effects if eaten in large quantities. This is because they can’t be fully metabolized in the digestive process, and can ferment in the intestines, which produces gas. 
Generally, sugar alcohols do not have much of an effect on blood sugar, though some sugar alcohols are different than others. If you are looking at a processed food advertised as, ‘sugar free,’ check to see which sugar alcohols are in it – because it’s quite likely there will be.
Erythritol is the lowest calorie, doesn’t tend to produce gas or bloating because it can be absorbed by the body (as long as it isn’t eaten in super high doses), doesn’t affect blood sugar or insulin, doesn’t produce cholesterol or triglycerides , and was actually shown to improve vascular function in type 2 diabetic patients. 
If you’re looking to use a sugar alcohol, go for xylitol or erythritol. These are hands-down the best options for your health.
Stevia is generally another good sweetener to replace sugar. Stevia can be produced naturally, and is calorie free.
From my literature searches, it seems that tagatose was once considered a drug for diabetes before being considered a food additive/sweetener. Tagatose has shown to improve body weight and HDL cholesterol levels  as well as regulate blood sugar after eating. 
Listening to a quick podcast by JJ Virgin the other day, she also made a point about Stevia. Since it is low calorie, it is possible that Stevia could trigger the same overconsumption effects in the brain that artificial sweeteners have shown to do.
Stevia and tagatose should generally be great sugar substitutes that won’t negatively effect blood sugar. Just watch out for any additives that the manufacturer might sneak in.
My Scientific Opinions
On Processing Sweeteners
As a chemist and scientist, I am not too concerned about the production of some sweeteners. Mostly here, I’m talking about the production of sugar alcohols and stevia. I’ve seen the production of sugar alcohols referenced as ‘industrial manufacturing.’ Which, yes, is true. But the industrial process is made with enzymes, and no harsh chemicals. The end product is sold in a purity you’d obtain from extracting it directly from a plant.
On Artificial Sweeteners
I generally don’t believe something is ‘bad’ until I see scientific evidence. But in some cases, there are lots of grey areas. Quite frankly, I don’t believe there are enough clinical studies on artificial sweeteners as there should be. Drugs undergo YEARS of clinical studies and research – yet these artificial sweeteners don’t. Artificial sweeteners should be classified and studied in the same way.
Maybe the FDA has cleared them because there is such overwhelming pressure from consumers to have their cake and eat it too (no pun intended). They want their sweets and processed food without the calories, and without outrageous costs. People will complain when the FDA does nothing about these potential risks, but people will complain if they are regulated or taken away. Sounds like a rock and a hard place.
On Making Choices
As a health enthusiast, I am aware of the facts, and I make choices. I choose not to consume artificial sweeteners, because they are man-made – not just manufactured, but man-CREATED.
If you cannot GROW IT, or it doesn’t come from something that was once alive, I don’t want to eat it. And you shouldn’t either.
However, I’m also not opposed to eating a manufactured sweetener – like Stevia or erthyritol as referenced above. I DO look to see if there are any other additives that I don’t want, but I am not too concerned about how they are made.
In terms of the sweeteners I always use, there are times when I choose to make something with a natural, full sugar, sweetener. And there are also times when I these other, healthier sweeteners. Though I am more and more leaning towards the latter.
So, What Sweetener Is Best?
If you are eating natural sugars, reach for real honey or maple syrup. Just do so in moderation. These have some (small) health benefits and are also lower in fructose. If you are looking for a substitute, try stevia or sugar alcohols xylitol or erythritol.
In the end – what we need to remember is moderation – or just not at all.
That is regardless of whether it is table sugar, a different variety of natural sweetener, artificial, or the ‘all healthy’ Stevia. It really doesn’t matter WHAT it is – it still needs to be treated with moderation – just like anything else.
References not linked above
 Ritter, Stephen K. The Case Against Sugar. C&EN Magazine, August 4, 2014, pg. 11-17.