I have been altering recipes for a while since my husband developed diabetes. He uses stevia quite a bit, but it has an aftertaste to me, so I have been blending stevia granules and xylitol granules (crystals) and sugar to give a great sweetness without the side effects for any of them, like the aftertaste. I have also found that in using these three together, I can reduce the total amount needed for the recipes and get the same sweetness as if I used just sugar.
I started by using one-third, one-third and one-third. I also started blending xylitol and sugar in my pantry so I am already getting a half-and-half ratio there. I am now finding that half stevia and half my blend works very well in the recipes I have tried so far, and I still reduce the total amount the original recipe calls for.
I order the xylitol and stevia crystals online. I also order the Truvia brand stevia, without the dextrose additive (they have two kinds for sale). Look for the white package with the green writing and make sure to check the ingredient listing to make sure you are getting the pure stevia kind.
And I order Sweetleaf Stevia, both drops and crystals for different uses. Stevia brands do have different tastes. We went through about five brands to find Sweetleaf has the least aftertaste. The part of the leaves and tree that are used makes a big difference in what you get in taste. Good luck!