Both kefir and kombucha are fermented foods that contain beneficial probiotics, and one is not necessarily better than the other. Kefir generally contains a higher amount of calories and may contain a bit more sugar than some kombuchas, but read the nutrition facts panel to verify sugar grams.  Kefir is most often made from milk, so it does contain dairy and would not be appropriate for someone with a milk allergy or lactose intolerance (though the process of fermentation reduces the overall lactose concentration of dairy products). Kefir can also be made from non-dairy liquids, such as water, fruit juice, or coconut water, which would be 100% lactose free.  Kefir made from milk does contain some nutrients that kombucha does not, including calcium and potassium. Kombucha does contain some caffeine since it is made from fermented tea, though levels are generally low (15 mg or less per serving).