I'd start with the cheapest. If that doesn't work, try a different one. There are many, many good products out there. It really all depends on what you want to do, as well as which parasites
you are exterminating. With some products, I have to take 4 times the recommended dose. With other products, the recommended dose will make me sick, sick, sick and I have to start with a lot less and slowly build up. Listen to your body. It will tell you what to do, and when you need to repeat the process. It will also tell you which products work best for you. Best bet is to find 2-3 products that work for you, and rotate them. Keeps the dang bugs confused and makes them miserable. That's what you want. Make them so miserable they have to leave. Exit. Down the toilet.