The dotFIT All Natural WheySmooth and BestPlantProtein both contain Stevia, but they are the only two protein powders that do.
Therefore, you can use WheySmooth, FirstString, Pre/Post Workout and Meal Replacement or LeanMR. We do not have a flavorless product, but most people use our vanilla flavored proteins in smoothies (I actually use the chocolate flavored WheySmooth in my smoothies). You will find some great dotFIT shake recipes including smoothies here.