This is up to your personal tastes! I like using a brut sparkling wine, which is dry, rather than on the sweeter side; this helps balance the drink so it doesn't end up tasting overly sweet. I used a brut Prosecco from the brand Mionetto. I would also recommend something affordable, rather than high-end, since you will be diluting it with the juice anyways! If you need some ideas, here is an article on choosing a sparkling wine for mimosas that I found helpful.