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To add to my previous reply:

Milk kefir is said to have a wider variety of organisms than water kefir, though both have a wider variety than yogurt. But water kefir is recommended if/since dairy protein is a problem for you. Homemade kefir is interesting/tricky-one batch will be silky smooth and luscious and the next one will be lumpy and tart-to-sour (if milk kefir). This is because the kefir grains are living organisms and respond to many factors (e.g., temperature of room/milk/water, changes in atmosphere...). Store bought kefir can be good as long as bottle says it contains living organisms.