Which is better? Master Pages or CSS or combination?

Hi all
I have spent time learning coding using master pages in inline styles and my sites are functional but look lousy. Now I am turning to learning CSS and to make my sites look more professional.
I wanted to try to convert my sites to using CSS. So I ask the question which is better option?
Also does anyone who develops in a corporation know if Master pages are use much?
 
thanks all 
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