In selecting potential licensees or buyers for your idea, look for people with knowledge of your product's market and the companies that serve it. It makes the most sense to approach people who have experience and resources in the appropriate industry. At the very least, these buyers will have a shorter learning curve than others and will have valuable contacts.
Don't overlook approaching the competition; they may know more than you about the market you're trying to enter. Competitors have the expertise to get the product manufactured and sold, and they're familiar with the best distribution channels.
The downside to approaching the competition is that they could use the information you give them against you. It is imperative that your idea have strong protection, such as a patent, and that you have a keen sense of how your competitors conduct business before approaching them.