There are plenty of good reasons to try rifaximin (Xifaxan) first, as long as your health program will pay for it. The other thing worth a try is a high-dose probiotic, like Visbiome Extra Strength. VSL #3 helps me significantly.
Although I generally prefer trying one antibiotic first, the fact that the combination of Cipro and Flagyl failed probably saved you a step (i.e. it's unlikely that either one alone would have worked), unless one of them is *causing* a problem.
Good luck, Peter!