A good way to write an article around a keyword is to research the things that google relates to the keyword itself. For instance, if I wrote an article about camaros, I found out later that when I ranked in search engines that google associates camaros with mustangs. So in my article, I might be able to tell a story about how I raced a mustang. I would not spam the keyword itself, I would use several synonyms and other similar related points.
Use a combination of both by mixing it up. If properly done you will be able to rank for both the keywords and then that would really help. Do a quick survey on Google and get an idea of which word will bring in the greater amount of traffic
Generally 2-3 words keywords are appropriate. Too lengthy key word phrases are not good as they are difficult to rank.
Yeah i agree with the above comments. A good article is one that focuses on the main keyword... if avatar review is also a main keyword, you can play with both within the article, but be careful not to keyword spam.