I've built a business solo, and I'm now building one with a co-founder. I can say, without hesitation, that the latter is better. I'm a lifetime loner, stupidly independent, and I don't play well with others, but having a co-founder is still a major net win for me. I'm lucky in that I've been working with my co-founder for years (I used to hire him for UI development work when I ran my previous company), so I know that our various skills and our personalities mesh well.

If you can't find a founder that fits well with you, and that you can trust not to screw you at the first opportunity, then going it alone is the only option. But, I'd recommend trying to find a co-founder. Sure, you can build a successful business solo...but it gives you much worse odds.