The success of a venture is going to have much more to do with WHO starts the company than whether or not there is one or more of them. Look at history and we see all kinds of successful companies that were started by sole founders on the one hand and more than one founder on the other. Maybe there is a statistical likelihood of a company being more successful if there is more than one founder... but no entrepreneur in their right mind is going to base their decisions on those kinds of stats. So much depends on the unique circumstances that you find yourself in. I particularly like this quote:

'But Grieselhuber argues that entrepreneurs should worry less about having "everything perfectly meet other people's criteria," and instead focus on, to quote Nike, "just doing it."'