I think that it's most important to have as many as bifidus as possible; and to take yogurt that has LIVE cultures, which no regular yogurt has. Only some organic "made from raw milk" and marked as "live cultures" is the real deal. the rest you may as well skip...
That's why kefir is a better bet - it has most bifidus and HAS to have live cultures. Also, only kefir also contains special type of candida which is (drum roll please!) BENEFICIAL for you. The only way to kill any type of mashroom is to invade it with it's enemy. So the candida from kefir is actually stronger then candida which we are all trying to get rid of. It's like that pharm medication - Nystatin. That's also a type of candida, just stronger then the one that causes problems.
So I recomend kefir and organic, non sterilized with live cultures yogurt which has nothing else except milk and cultures. No additives of any kind. IF you need fruits in there -add them yourself, preferably organic.