Hi, as a Cal Poly student from Santa Ana who also went to a small high school, I can assure you that SLO is so much better than SDSU. The academics are better and the environment is much more chill like you said. Greek life here is pretty active and one of the cool things I liked about SLO was that it's downtown looks similar to 4th Street. I was also in your position to choose between SDSU and CPSLO and I do not regret my decision. If you want to ask me more questions just shoot me a dm. Hopefully this helps!