https://nextstrain.org/ncov shows there is a massive number of genetic variants. I have yet to see anyone successfully show that the variants have different behaviours, as that is hard to do. However any strains that are more contagious should dominate over other strains.

Due to international travel, and especially citizens returning home, the different strains are coexisting within the same country.

They have even used strains and genetic trees to trace individuals that transmitted the virus.