I just tried Kefir fir the first time. The bottle says 15 billion per serving.
I normally use chobani greek yogurt. (I don't have a tub in front of me, but I don't remember if it ever mentioned counts).
So, what has more probiotic power? (Kefir vs. Greek Yogurt)???
In general, kefir--either dairy or water--has many more species of beneficial flora than yogurt. The marketing of "16 million" doesn't touch on how many species. I've read that good yogurt will have 2-5 species (with large total counts) while kefir may have dozens.
Kefir and kombucha are more powerful--so much so that it's advisable to start with very small daily doses while such caution is frequently not necessary with yogurt.
I'm Greek too, and make my Home-made Greek yogurt (Yiayia's recipe), kefir (milk and water), sauerkraut, and many cheeses. Recently (5-Mar-2013) I had Warren Analytical Labratories of Greeley, Colorado, USA assay some of my ferments for "Lactic Acid Bacteria MB 075 (Spiral)", here are the results:
1) Milk Kefir -- 2.6 Billion Colony Forming Units per milliliter (CFU/ml); 2) Water Kefir -- 1.2 Billion CFU/ml; 3) Greek Yogurt -- 60 Million CFU/gram (note for water, 1 milliliter = 1 gram); 4) Cabbage Sauerkraut -- 5.3 Million CFU/gram; and, 5) Health-Food-Store-bought Greek yogurt -- 1.1 Million CFU/gram.
I make my ferments for less than $8 per gallon, and believe highly-processed store-bought probiotic ferments and pills are outragelessly expensive. Learn to ferment real delicious food and live healthy like Mediterranean people often do.
I don't think it truly matters - I think you're reading into the marketing hype. 14 megapixels! 18 megapixels! It's a good idea to diversify your probioitc sources, so the best move would be to enjoy some of each, and also try some kombucha, sauerkraut, kimchi, etc..
Real kefir (not store-bought, which doesn't contain yeasts) is a super-food, with up to 40 different strains of yeasts & bacteria. Consider that I'm Greek, but I root for Kefir.
I read somewhere that a cup of yogurt contains up to 1 trillion bacteria, and kefir up to 5 trillion, I don't know if these numbers are correct though.
Greek yogurt has most of the whey strained off, and I believe that's where a lot of the bacteria reside (I'm not 100% on this, but fairly certain). Kefir FTW!
Depending on how long the product has been sitting on the shelf also reflects the probiotic strength,so if you have fresher yogurt and not so fresh kefir,I'd go with the yogurt.But in general kefir has more strains.I make both at home and from experience know that some organic yogurts are dead,because the don't work as a starter.So,I guess it depends on the brand
Kefir grains grow into a cauliflower like glob. I bought mine on eBay: http://www.ebay.com/sch/i.html?_trksid=p3984.m570.l1311.R11.TR11.TRC1&_nkw=kefir+culture&_sacat=0&_from=R40
These folks have a useful screen container to grow it in: http://www.culturesforhealth.com/milk-kefir-starter-kit.html
You can use milk or water, though I prefer raw goat milk. Let the milk reach room temperature (unless you're getting it straight from the goat), add the grains or clump. It should ferment at room temperature for about 30 hrs to be most beneficial. (See Restoring Your Digestive Health by Jordan S. Rubin, NMD and Joseph Brasco, MD).
After that time (actually I taste test mine), I remove the clump, freeze with a little goat milk in a plastic container for next time and refrigerate the kefir.
Just yesterday I took the store bought stuff (which just tastes like runny yogurt) and put some clumps in it for about 48 hrs. It improved the flavor and now tastes like actual kefir.
It does continue to grow in the refrigerator, but at a much slower rate.