Any and all - the goal here isn't typically to select specific keywords, but instead to create lots of high quality content that naturally targets interesting/searched-for terms. Instead of singular optimization on specific terms, the focus is on accessibility and best practices throughout the site to earn traffic through both high volume and long tail queries. Concentrate efforts on great content, and use keyword-based optimization only as a secondary method to confirm the titles/headlines of the works you create.
To bring high rank in the SERPs for your website must be the first and foremost goal of SEO. White hat SEO (Ethical SEO) should be the first choice for you as it is the only method which does not involve deception.