If you were to meet your clone, what would you say? What would there be to say? For how long would you just stand there, dumbstruck, and speechless? The same history, the same personality, the same conclusions drawn. Throw out the pointless questions of which one is real, or how did it happen; the concept is far more intriguing than the cause, but it is the cause which so many people get so hung up on.
Yourself; simultaneously the best and worst possible person to be with. Together, you know exactly how you want to do things, and could achieve greatness with perfect syngery, but in theory only. In reality, two of yourself is no better than one. The same bad idea twice is still a bad idea, and how can you tell yourself that you’re wrong if you don’t know the answer? Like selective inbreeding, you bring nothing new to the table by copying yourself; you close yourself off from new information and new ideas. When you disagree, you will disagree for the same reasons, at the same time. It is not a disagreement with yourself, but with the world, with the current state of things. To truly disagree with yourself would be to have doubts, pure and simple.
The truth of the matter is, you already have a clone of yourself in your head. You can easily talk to yourself and answer back, or write down your thoughts and read them as if somebody else wrote the words. That you yourself are making up the responses to the actions within your own mind is irrelevant, because would a true clone respond any differently?