I was told by the smoothie eaters that it’s too tangy and not sweet enough and they prefer vanilla regular yogurt to greek yogurt.

They don’t know what they’re talking about. Taste-wise, Greek yogurt is just thicker than regular yogurt, and plain yogurt simply doesn’t have the sweeteners and flavors added.

You can easily modify that yourself by adding sweetener of choice and whatever flavoring you like, such as vanilla extract. Just do it to taste and you’ll be fine for smoothies.