There are a couple of arguments about keywords, in that there are “buying” keywords, and simply “browsing” keywords. A browsing keyword can be long or short tail, and will usually be easy to rank for. Browsing keywords have the main niche keyword in them, but unfortunately there will not be much traffic that will convert. On the other hand, these keywords attract visitors who will click AdSense ads and other links on your page in their pursuit for information about the niche subject.
Buying keywords are often much harder to compete with in the top 10, but they will of course provide better results when you are looking at selling a product on your website (via affiliate link or otherwise). The reason they are more likely to purchase is they have already decided that they want the product, as they are looking for the last phase of the search – a place to get what they want. All you need to do is provide the final step in that equation, and give them an easy way to get to what they want.
Buying vs. Browsing is always a hard choice to make. The traffic you get from browsing keywords could, in theory, convert into paying traffic. The buying keywords are harder to rank for, therefore will take much longer to appear – despite the best will in the world with SEO. The browsing keywords will be quicker to rank for, and of course once your site is ranking you can make it easier for yourself to rank for the buying keywords. Its a very big swings and roundabouts game, and we just have to take a risk more often than not.
The risk can be calculated usually by the product you are trying to get traffic for in the first place. For example, if you were looking to use a browsing keyword for a product that had a free trial on a CPA network, then logic states that anyone interested in the product will want to take up a free trial. However, a product that you have to buy outright will not do so well to the browsing visitor. AdSense would work much better as a way to monetize your site – because the AdSense ads will send them to other sites to find out more information.
When you are weighing up the pros and cons of your keyword, you should take your market and your product into account, and work out how you can convert every single visitor. Naturally this is impossible – but trying to please everyone will ensure you are at least pleasing someone!