For me, Star Trek wins hands down. The reason is realism and agelessness. Very little of the science and technology portrayed by even the earliest Star Trek series (1960s) has become outdated. Even the shape of USS Enterprise is ageless.
Others may have reasons for choosing other series. For instance, the Star Wars movies are hugely entertaining, and if you choose them for that reason, fine. I accept that.
However, for those who like realism, there were many flaws in Star Wars even when the first movie was made. People carrying heavy loads by hand in an age when they could flit from star to star at will. Light sabres that can do no more than a samurai sword. Energy-bolt handguns that are no more effective than a .45 pistol. The list goes on and on.
Off-topic here, but among non-series sci-fi, Close Encounters of the Third Kind is one of my top favourites.