Sucralose (brand: Splenda) still has (well, to me anyway) a nasty aftertaste, not much different from aspartame or saccharine. Also agree that Stevia in pretty much all forms has a very strong licorice aftertaste.

Though true diabetics might see a SLIGHT difference in blood chemistry between agave and say, sugar, agave is still mostly fructose hence: sugar. It's not really very different from honey, although it's frequently touted as having a low glyecmic index and hence "better" for you, but I've read articles challenging that. I regularly cook for a neighbor who is diabetic and stopped using it because of the uncertainty.

Both erythritol and xylitol (sugar alcohols) are available in granular forms for sweetening things like coffee or tea. They have no impact on blood sugar levels so they are sometimes recommended for diabetics. Some people have, errr, unpleasant side effects from sugar alcohols, although not usually from the teaspoon and smaller doses used to sweeten coffee or tea.