CBD is an isomer of THC, which means they share the same molecular formula, but have different structural formulas. Basically they are made up of the exact same molecules, except that the molecules are connected in different orders.

CBD by itself has no psychoactive properties(CBD by itself does not get you high), however it does regulate the euphoric effect of THC and gives it more of a sedative effect(more of a "chill" high). Cannabis often has a high CBD content (as much or more than 40% CBD in most Cannabis extracts)

On the other hand, THC is intoxicating on its own, and normally gives a more stimulated high.

To some things up, If you want a more energetic high, you want more THC and less CBD, usually Sativa and sativa dominant hybrids have more THC and less CBD. If you want a more relaxed high, then of course your want more CBD, usually found in Indica and indica dominant hybrids. But dont forget CBD on its own does nothing, it only regulates effects of the THC high, so regardless you want a high THC content, the difference is the ratio of CBD to THC.

Since most of us dont have a chemistry lab in our homes I dont think you'll be able to find exact info for CBD to THC ratios on most strains.

General rule of thumb, Sativa has higher THC to CBD ratio, whereas, Indica tends to have higher CBD to THC ratio.