Do you have a series of nesting serving bowls that all look the same, but hold differing quantities of food? If you don't have one and like a more unified look, going for a nesting set of serving bowls can help remove busyness from your table and allow you to concentrate on the food instead of the bowl.
If you're looking for a more cohesive look, selecting a set of nesting glass or ceramic bowls are wonderful for serving (or for a decorative mise-en-place if you like cooking!). Nesting wooden bowls, on the other hand, are perfect for entertaining: Set a small set of wooden bowls by a large bowl of chips, and your snack station is good to go!
Everyone should have at least one large mixing bowl for the kitchen (one made of metal or plastic) and one large serving bowl, even if you just use it to display fruit on your kitchen counter. However, the best set or size of serving bowls for you to choose will depend on how often you entertain - and how many people you have to serve! If you frequently host more than 5-7 people, you should have at least two large serving bowls, two or three medium ones, and 5-7 smaller ones. That way, you'll be able to take care of you and your guests, no matter what you happen to be serving.