There are two major strains of cannabis: Sativa and Indica. In addition, there are hybrid strains of varying tendencies: leaning Sativa or leaning Indica.
Which one you choose is determined by what you are interested in accomplishing: up mood or down, working the body or mind, bringing about energizing or calming energy.
Sativa tends to be a mind high. Bringing creativity to the fore. Uplifting.
Indica tends to be a body high. Relaxation and calming are felt. Grounding.
The hybrids can do either or both depending on the strain. There are Sativa-leaning hybrids and Indica-leaning ones. These are cross strains which have been developed, some over years, through many plant generations.
There is a wealth of choices out there. Sativa, indica or hybrid.
If you are clear with what you want to achieve, which strain to choose will be easier to decide.