I don't take a probiotic. I find they are all too expensive, and they don't work.
I have started taking a natural probiotic - unpasteurized apple cider vinegar. A tea spoon in a glass of water or juice a few times a day. I also like to put a little on my salad with extra virgin olive oil. Unpasteurized apple cider vinegar is a natural probiotic, it has friendly bacteria. It's also known for curing constipation as well, if taken regularily.