It is better to be intelligent or sexy? For scientist is important to be intelligent. For model is important sexy appereance. For school professor is important to be intelligent. It is better to be intelligent or sexy to achieve the succes in relations to other people.
Then, the web application should be intelligent or sexy? IMO, It's same with above. A search engine should be intelligent enough to bring you the best information based on what you mean. A entertainment applications should be sexy, fresh, suggestive to provide more fun.
We can find that examples of these character from google.com and youtube.com.