What should be the optimum keyword density number for a good content??
In my opinion the keyword density must be between 1-3%.
Around 4% is the upper limit I have heard. Above that, and the article can start to sound spammy. But I agree that 1 to 3% is best.
Keyword Density for Web page content 2-3 %
Keyword Density for Articles 3-4%
KEyword Density for Press Release 4-5%