There have been alot of people raising eyebrows about the low glycemic index wonder sweetener agave. Some one who brought up a case against it was Dr. Mercola (see my blog on Dr. Mercola)

It makes sense to me that agave is not good for every "body" because, in terms of Ayurveda, Agave or cactus-is not a plant local to my climate (Michigan) and I also imagine it would have a cooling effect, which would be detrimental to some one who was kapha or vata.
When treating people I tend to stick with native herbs and with only a few Ayurveda/Indian additions.
Also, I have some reservations about stevia, I find quite a few people having reactions to it and many people are using the convenient "white" powder form of stevia, this is in fact stevioside.
Stevioside - is an isolated extract, and is considered purer than aspartame and NutraSweet. However, it is also the most highly processed and denatured of the available products. From a nutritional point of view, it is not a good choice. As it is a a refined white product and has been molecularly changed.