A lot of good ideas and comments out there. This question has been posed ever since I have been in the martial arts, and I am sure its been around far longer than that.
I think you guys are on the money when you talk about no one system holding the key to success for everyone. It does depend on the practioner.
That said, I have always thought it to be somewhat naive to merely say striking is the way to go, or all fights end on the ground or whatnot. The bottom line is that conflict can involve any combination of strikes, chokes, throws, locks, ground fighting, weapons, etc. I think it is important to be knowledgable in all these areas. By studying all these areas, one not only becomes acclimated to all areas they may face, but they also have more choices to develop a strategy, box a wrestler, wrestle a boxer.
The downfall, if that is what you want to call it, of most "styles" is that they only take into account a small area of conflict, such as your striking arts, and beat it to death. Let's face it, judo is a wonderful art, but do you really need all those throws? The answer is of course not. Two or three will surely suffice.
So my advice, is instead of looking at any one particular style, look to become familiar with all areas of conflict. Combine this with good training methods, ie. lots of randori, and you'll be best prepared to face what may come your way.