Typically you will want to pick a keyword that has a strong relevance to your product and also has the largest search volume possible. The more searches a keyword has, typically the more sales will be generated through the search term. That said, you do still want to make sure that the keyword you are targeting is directly relevant and that products that are showing up in the results are consistent with your product offering.
You can use a tool like Keyword Research to identify a relevant keyword with high search volume.