Unless I am mistaken you are asking which is better for treating your Candida - milk kefir grains or water kefir grains?
Milk Kefir Grains are said to have come to us from the ancient land of Caucasus which is said to have been named after one of Noah's grandsons. There is also a connection to the word Caucasian which, for some strange historical reason I do not quite understand, is used by law folks to specifically identify a type of white people. Be this as it may, milk is generally characterized as being a shade of white. If you compare the color of milk kefir / milk kefir grains to the color of milk, you might say they are close to the same color. Here is a photo for example. In a similar fashion, the color of water kefir grains might be said to be close to the color of water. The sugar content for growing Milk Kefir is mostly provided as a natural substance contained in milk, be it cow milk, goat milk or other milk such as coconut....except, in my way of thinking, coconut milk is not really milk in this same context but is really coconut water.....just saying "coconut milk " may be an examplle of water that contains a natural abundance of sugar. As such, you start off with a source of milk kefir grains, sometimes referred to as the mother culture ( similar to live fermented apple cider which is also known as apple cider vinegar ), and then you place these grains into goat milk or cow milk for a day or so. The kefir grains are a live fermen. The sugar content in the milk helps to promote the fermentation process so that after 12 to 24 hours, the milk is no longer plain milk but is instead fermented milk which you then strain so that the milk is consumed and the grains are then put into another batch of fresh milk so as to repeat the process.
There is another kind of kefir grains that some people call Sugar Grains or Sugar Kefir. While similar to milk kefir grains, water grains are distinctly different. For one they are not white " caucasian ", they are translucent. Another difference is that Sugar Grains are not placed into milk, they are placed into water and the water has sugar added to it. Whereas milk naturally contains enough sugar to promote the fermentation effect that is Kefir, water grains need to have sugar added to the water since water itself does not naturally contain much sugar.
As to which one is better for treating this or that, such as for treating Candida overgrowth, based on my limited understanding, there is no absolute answer. There is much debate on this question....the jury is still out, so to speak....your mileage may vary. Some people believe that Water Kefir is better for improving conditions such as Candida overgrowth but this belief may in part be influenced by the belief that adult people should generally avoid consumption of dairy products IE> milk. I do not disagree with this belief but neither do I agree with it. Ultimately, you should be the one to determine which is best for you..... but this will require you to try it out, make you own tests and based upon the results you experience you can decide the best way for you to answer the question. It may be that Water Kefir is best for your condition....and maybe Milk Kefir is best for somebody else and their condition. Good luck!