NOTE TO READERS: Although I do like writing snail mail, sometimes e-mail is much more efficient. Tamara, a whip-smart woman I used to work with, got back to me right away with a really helpful answer that sheds a lot of light on the subject of yogurt (and it's frightening what some food processors will do). What do you think?
You raise an excellent question!
All yogurt will contain some natural milk sugar (lactose), even if it is unsweetened. As a rule, a typical 6 oz container of plain, American-style yogurt will contain about 11g of natural sugar (or, 1.8g/oz). A typical 5.3oz container of Greek-style strained yogurt will contain 6g of natural sugar (it loses some of the lactose in the watery liquid that is removed from the straining process).
Any sugar in your yogurt beyond these naturally-existing levels is added sugar.
So how much is too much? Well, keep in mind that every 4g of sugar is a teaspoon. Most experts agree that a reasonable upper limit for added sugar in a healthy diet would be about 10 tsp/day... though bear in mind that this refers to a "typical" 2,000 calorie diet, which is more than many women are eating (or should be). 5-9 tsps added sugar per day is more realistic (nutritionally, but probably not in practice) for many women.
So the question is: how do you want to spend your added sugar budget? If you don't drink sweetened drinks (including your morning coffee/tea) and rarely have desserts/sweets, etc.., then maybe you can afford to spend a few tsps of sugar on that breakfast yogurt. But even so, many choices still seem excessive.
Among the yogurts you inquired about, The Cultural Revolution yogurt at 11g for a flavored 6oz variety is a great option... and I love that it's organic as well. (It appears they produce a greek-ish style yogurt which is how they keep the total sugar low even though they add additional). A few brands you mentioned (Better Whey, Cascade Fresh) had 14g-16g sugar for a 6oz container; that's like 3-5g added sugar, or ~1 tsp. I find that pretty reasonable if you're going for a flavored yogurt instead of plain. Another good choice for flavored yogurt is Siggi's Icelandic Style Skyr (10-11g sugar per 6oz).
Once you get much past the 16g of sugar range for a 6oz yogurt, I tend to think it's a bit much, and might advise you to try buying plain (or even better, plain Greek yogurt) and adding 1 tsp honey per 6-8oz to sweeten it yourself. By this guideline, you'll probably disqualify 90% of the yogurts sold in the supermarket.
In other words, the Activia at 17g (per tiny 4oz container, no less) is outrageously high...it has 2.5tsp of added sugar in that itty bitty little container. If you like the 4oz size, I'd recommend Stonyfield Farms Yo Baby yogurt; it has 12g sugar (~1 tsp added) per container, which makes it more appropriate for adults than babies, anyway.
Another big offender in my book includes the Stonyfield Farms Organic flavored varieties, which typically have 21-23g sugar per 6oz serving (again, that's 2.5-3 tsps of added sugar!).
As far as your question about the different types of sweeteners, there's no real difference between sugar, high fructose corn syrup, or fruit juice concentrate as far as how your body metabolizes them. No source is any better or worse than the other. So don't be fooled by "organic cane sugar" on an ingredient list as being somehown benign or healthier. Straight fructose (or higher-fructose sweeteners like Agave) is metabolized differently than the other sugars, but for the quantity found in a 6oz yogurt, it doesn't make a measurable difference one way or the other for good or for bad. Sugar is sugar is sugar. Having said that, I'd take real sugar over those artifical sweeteners in the diet yogurts any day; at least your body knows what to do with it. I avoid aspartame and acesulfame potassium in all foods and drinks as a rule. The only time I think these products are acceptable is for people with diabetes who need to strictly avoid sugar for glycemic control reasons, and even then, I'd recommend trying to develop a taste for a plain yogurt or (even better) plain Greek yogurt first before resorting to the artificial stuff.
Hope this helps clear things up! It makes me sad that our supermarket has become so complex that highly intelligent, educated people need to consult nutrition experts just to navigate the yogurt aisle... but I'm glad I could help in any event.