you are going to start is probably Psilocybe cubensis
as it is the easiest to grow of all mushroom species indoor.
As for which P. cubensis strain
this is a question that keeps coming up, but can never be really answered. It is one of the truly subjective questions in the hobby, on which *everyone* will have their own answers.
Please refer to the Strain Guide
But is there one magic strain that will give you lots and lots of really super potent mushrooms in a quick amount of time? No, there's not, plain and simple. Some strains may be judged subjectively by others to be more potent than others, and some strains may be judged to be bigger and produce a heavier weight.
But comparing P. cubensis to P. cubensis generally, there is not a "super strain" which should be chosen for any particular reason over another.
There is no consensus as to "the" strain to grow, and you won't find one. Some people like redheads, while some prefer brunettes. It's just that subjective.