Kefir vs Yogurt compared side by side. Learn which of the two fermented milk products is better. Kefir is a fermented milk drink, similar to yogurt, with a milder taste and a different probiotic composition. Kefir is considered to be better as a probiotic food, because of the bacterial profile used to ferment it. Many people prefer the less tart taste of kefir, but other people like yogurt better.