I was previously using 960GS as my starting point and Bootstrap is a significant improvement because it comes with better default theming and the LESS layout is

I was previously using 960GS as my starting point and Bootstrap is a significant improvement because it comes with better default theming and the LESS layout is robust so I can churn out better looking designs quicker. It's also more flexible since you can specify an arbitrary number of columns not just 12 16 or 24.