Prosecco or non alcoholic prosecco is sweeter than champagne. Choose that if you like a sweeter mimosa. Choose champagne (or cava) for a less sweet mimosa. Cava is a less expensive, great alternative to champagne. For a mimosa mocktail, use citrus sparkling water, soda like Fresca, or non alcoholic cava or champagne for a less sweet drink. Prosecco or citrus soda for more sweet. You can also add more orange juice to make it sweeter.