Obviously, Black tea is most common, most popular and widely consumed across the Globe. It's so rich in aroma and well known for flavor whether consumed with milk or without milk. One can skip the addition of sweetener altogether but the use of sugar or even jaggery is not uncommon.

Next popular type is probably Green tea and ideally consumed with lime/lemon juice added into it. It can be served as hot or cold beverage. I don't have exact data with me but it will not be far from reality if percentage wise it is 70: 20: 4: 6 for Black: Green: Oolong: White tea consumption worldwide is considered. When it comes to Herbal tea it doesn't fit the definition of tea which is a product derived from Thea plant. Different types of flowers, leaves etc. goes into preparation of decoction which is termed as tea and in my opinion it is a misnomer.