I've grown a good amount of CBD strains and would suggest trying a few different breeders and ratios. If you just want to try one and see how it is, go for a 1:1 or a 2:1 (CBD:THC).
A true 20:1's effects won't satisfy most people, but could be perfect when mixed in with a standard high thc strain.
Can be good to have a few ratios on hand to make the right mix.
From my experience CBD Crew is top notch, also Dynafem, Expert Seeds, Barneys Farm. Very frosty and some of the best terps around.
Seeds said to be "CBD Rich" wont always be consistent with their reported ratio, but should have a decent % of CBD. (random distribution)
Clones are the way to go if you want to know exactly what you are getting.
Also, the same genotype(clone) could easily range from 1:1 and 3:1 (or more) depending on how its grown and other environmental conditions.
Good luck!