Agave nectar and honey are both natural.
Saccharin(Sweet & Low), aspartame(NutraSweet/Equal), and sucralose (Splenda) are all chemical compounds that don't break down the same way natural sugars do. There was a chemist that had studied one or maybe 2 of the artificial sweeteners for one of the national news shows. His conclusion was that in the testing samples they were "safe", but then he added "You won't see me eat or drink anything with these chemicals in them willingly." His attitude was basically, that we make our own choices about what we think is healthy and substitutes may be more dangerous than the effects of the natural counterparts.
I believe obesity and diabetes are hereditary traits that can both be prevented or delayed through lifestyle change. Chemical makeup of your gut can actually cause hunger cravings, metabolic change, and psych issues because serotonin is produced there. (depression goes hand in hand with obesity, often) There are skinny people with type-2 diabetes, so you can't always link the two. If your body doesn't break down the sugar in your blood, it can basically cause all kinds of damage to your blood vessels. Dr. Oz did a demonstration with shards of broken glass to symbolize sugar crystals in your bloodstream floating around and that areas furthest from the heart where circulation is poor typically end up with the most damage.