Clarkia is definitely Hulda Clark 's product. I hear that it is a bit more expensive but good. Let me see if I can find you a link. I also know that many people have tried Paraway.
I was the one who used the one from nowfoods.com. I was all set to order my own bottle of Clarkia but then I got all impatient and there just happened to be a nice huge 2 oz bottle of the nowfoods stuff at my health food store. So instead of researching, I took a big chance and bought it. But I did notice that it had all 3 of the main ingredients in it (green Black-Walnut hull, Wormwood , and clove). When I took it, I noticed it was really strong, which was good. And, after only 2 days of taking it I got out those creatures from another planet, so I am definitely set personally on using the nowfoods one.
Hope that helps! Sorry I can't be of more help with the other parasite products - maybe someone here will chime in.