Just from my personal perspective, I'm a big fan of buying a business that has been a little neglected, but appears to have a reasonable foundation. You get the infrastructure already there, at least some customers to start with, and some revenue from day 1. If the business has been a little neglected or poorly managed by the previous owner, then you should be able to purchase as a suitably reduced price.
As MC3033 said, a new development is going to take a long time before it actually produces any income. I applaud those who have the patience, persistence and courage for a new development, but it's not for me. I certainly prefer to improve and build on existing operation.