This one really comes down to personal taste and depends on whether you will be serving food alongside the Champagne. Champagnes are categorized according to their sugar level, with extra brut (the most dry), brut, extra dry, sec, demi-sec and doux (very sweet, considered a dessert wine). A dry Champagne pairs well with appetizers such as sushi or other salty snacks. A mid-sweet Champagne works best with cakes and other sweet foods, so this would be a good choice for a garden tea party. The most common style these days is brut Champagne but look out for other styles so you can experiment and see which one you like most.