I wouldn`t bother with the yogurts, specially big brands like activia. These companies spend more on advertisement then the actual product. Also, they add preservatives , gelatin and other additives to maintain texture, flavors and extend shelf life etc. The best and strongest yogurt is home made and eaten fresh. Its pretty easy to make Yogurt or lacto fermented foods like sauerkraut.
The best probiotics I have found were human micro flora(HMF), strains derived from the human body. They are capable of adhering to the gut lining easier as apposed to animal or plant derived strains wich may be considered foreign to the body.
Keep in mind it is very, very difficult to fully restore the intestinal flora to its original state. If you have ever been nuked by Antibiotics or suffer from candida or leaky gut then the conditions for flora restoration is minimal. probiotics will aid in digestion and other things certainly but the effects will most likely diminish after discontinuation.