They both taste delicious, like a butter sugar cookie with lots of cinnamon. But the higher acidity of the cream of tartar imparts the traditional snickerdoodles a tangy flavor, a bit metallic, while the baking powder causes them to be milder. This is why I prefer to use baking powder instead of cream of tartar. Also, the snickerdoodles without cream of tartar are slightly less puffy but still puffy enough; just have a look at the pictures.