keywords are more important or quality??

How many times keyword should be repeated in a 400 words article? Content must be more informative, quality centric or keyword managed?

Just write the article and make sure it adds value. Do not worry about the keyword %. If it takes you 30% to get your point across or 1% it's all relative to the information.

Exactly what fxphil said. Also if your keyword density is lower but your story is written better you have several advantages:
- Readers will more likely share your stories.
- Readers will more likely come back to read more.
- You will also get indexed in several other keywords by google which will give you overal stable traffic from google and/or
other search engines.