I've used Bowtrol. That's the only one I've used. I didn't like it very much, and I wouldn't recommend it. I don't know much about the different herbs, but I read that it has two different ingredients that can cause bowel damage. I don't think Bowtrol worked very well, but I don't really have anything to compare it too.
I have heard good things about both oxypowder and colonix. I'm actually looking to try one of those, but not sure which yet. But everything I've read online was pretty good.