Xylitol has been shown to have a positive effect on dental health (something to do with inhibiting a specific type of bacteria) whereas stevia does not. I think stevia is a little more bitter. We use a product from the supermarket which is very finely raw sugar combined with just enough of the stevia to double its sweetness - so you're more than halving the sugar intake without the bitterness and you still get that nice raw sugar fragrance too.