As an SEO consultant I would have to suggest using phrases (never words) and also optimizing for every variation.
If this gets a bit cumbersome for 1 page you can always split them up on different pages. In the long run this will help you a LOT more since you will have very targeted pages with highly optimized terms.
The above comments are true with regards to meta keywords however the TITLE tag and to a much lesser degree META Description can still be important. Again another reason why its good to split the keywords out and optimize the PAGE content (or keyword density) for each phrase.