Get back to me after you read or listen to this book. It reviews all of the theories in depth.
While Oswald was a pretty good marksman as recently as four years before Kennedy was killed, he was clearly on a downward trajectory. But he was also clearly the best patsy available for the deep state.
The Nelson book is probably one of the most comprehensive books available on the topic. It may have minor imperfections, but it is a little more than a decade old and uses sources other than a cherry picked "Warren Commission" trying to rush a deep state coverup to print in time to ensure LBJ's landslide re-election just months after he orchestrated the JFK assassination.
Unlike other conspiracy books which start with a foregone conclusion and cherry pick data to support that conclusion (hello, Warren Report), Nelson's book examines the evidence comprehensively and reaches the only logical conclusion.