Whatever keywords your using but they must be appealing and attractive so that people can come to visit your site...
Mostly it is depend on the types of website and business. Keywords should be competitive and attractive. So i think Key Phrase types keywords are very useful and good.
A mixture of long tail and short tail would do the job. Usually the long tail keywords are searched by less people, but you'll have more chance of getting traffic from them as they have less competition.
Basically Keywords classify in to two categories: Competitive Keywords and Phrases "Long Tail Key phrases". Long Tail Key phrases contain more than three words and that make up a phrase. phrase specify your product or exactly what you want to sell. And whenever customer finding specific search pharse then it help to goes very closer to that product.most probably the long tail keywords are searched by less people, but you may find there more traffic from them as they have less competition. But in short keyword it does work exactly oppsite...so i think long tail keyword is more useful than short keyword.