I'm currently using something called HMF Forte after it was recommended to me by my local naturopathic doctor. They are pricey little buggers but I find them to be effective. Here is a link.
Before this, I used to use a brand called Udo's Choice. I didn't switch brands for any particular reason, I just decided to try something different.
I'm not sure a "best probiotic" really exists. I'm a firm believer that it doesn't particularly matter which brand you use, as long as one is taking some type of live bacteria or probiotic, it's beneficial for the bowel.