What should I look for in a Probiotic?

You should find some in your local health food store or whole foods etc. Buy the type that need to be refrigerated rather than the pills. They are more effective as probiotics are alive and are more active in that form then dried out and pressed into pills.

I'm happy with the Primadophilus Reuteri made by natures way, they need to be kept in the fridge.

:)

The first consideration is the survival rate of your bacteria. Between 90 and 99.9% of the bacteria in a supplement are destroyed by your digestive juices. The advice about when to take the probiotics to achieve the best survival is conflicting, but the bottle I looked at last said to take them after eating and I have also seen that advice in other places. I have only found one commonly available enteric coated probiotic: "Ultimate Protec Multi Probiotic" by Natural Factors. I think that it is worth the small extra cost to get ten times the viable probiotics into the gut. It was in my local health food store, but you should phone to check since not all stores carry the different brands. It cost $28 for 90 caps (and it needs to be refrigerated). You may be able to find other brands that make an enteric coated probiotic, so ask about that if they don't have the Natural Factors one.