My wife and I watch both.
The Mentalist is super. It is basically just a vehicle to showcase Simon Baker, and he's simply excellent, as a former "psychic" who now campaign against such charlatanism, and applies his skills of observation and detection, that served him so well when he was a charlatan, toward solving complex crimes.
The Good Wife is also very good. It is also mostly a star vehicle, showcasing Juliana Margolies, but some of the other actors in the show are as good as she is, and so it has more of an ensemble feel. Margolies plays the wife of a man who was state's attorney and was caught in a sex scandal. Disgraced, he was convicted and jailed, and she was forced to dust off her hardly used law degree and become a junior associate at a college friend's law firm.
The Mentalist can probably be picked up at any time, from anywhere, while The Good Wife really should be watched from the beginning and in order.