Starting a business you plan to run for the long haul involves long hours, potential sacrifices (financial and personal), and lots and lots of hard work.
The best thing is to find something you're really interested in. Something that makes your eyes light up, something that makes you jump out of bed in the morning ready to go, something that you'd stay up all night working on even if it weren't your business. The more enthusiastic you are about what you're doing, the more enthusiastic your potential customers will be.
If you already have a few vending machines, and that seems to be working for you, why not expand on that? Or if that doesn't get you excited, figure out what will, and work on that.
So, what's your passion?