The most important deciding factor, in my opinion, to narrowing down CBD strains is to figure out what ratio of THC to CBD works for you. The most common strains (easiest to find) seem to be the 20:1 (roughly) CBD to THC strains. Strains such as ACDC, Cannatonic, Charlotte's Web etc. Personally I prefer 1:1 ratio strains but even 4 or 5:1 CBD to ThC strains are good too. I find that the closer you can get to a 1:1 ratio of CBD to THC is best for pain relief. I like 1:1 strains like Pennywise or Midnight. A good 4 or 5:1 strain is Critical Cure. My understanding is that the 20:1 or so strains that have 1% THC at best are mostly used to treat seizures but you really need some THC on par with the CBD levels if ou are going for pain relief.
This is just what I've read and found out myself. I suggest trying all sorts of strains til you find the ratio that works. CBD Moby Dick, Sunkist, Pennywise, Critical Cure, Cannatonic, ACDC, Charlotte;s Web, Midnight...