You need to just start trying a few. I personally started with TGA Subcool seeds because one strain was recommended to me because I was looking for very specific smoke attributes (anti-depressant, ZERO paranoia, no couch-lock) and one of his strains came up a couple of times. Since then, I have bought four more strains. On his site he has very good descriptions of what the smoke is good for treating.
Since I'm growing for specific high attributes, it's important to me that the descriptions of the high are spot on. "Great high!" "I got baked!" aren't reviews that are going to attract me to a strain. "Happy, social high with mild pain relief" will.
All the strains I like are sativa dominant -- so that eliminates a lot of breeding stock for me.
Just start a few -- I order from Hemp Depot, and they seem to have good breeders in their offerings.