My first choice is to fish alone, always. I can concentrate 100% on what I need to do to succeed. There is always a pressure when taking out someone else, and you have to consider their schedule and input into the decisions thru the day. I am introvert like some folks above, and the solitude is something I need. I like going by my own schedule, making the decisions, and positioning the boat so I can get the best cast angle.
Granted, the odd time I fish with people close to me, like my wife, my Dad, my best friend, it is fulfilling in a different way and very rewarding. But, I couldn't do it every day.