Where should I need to save for new CSS file for master page in shareopint

Hi Everyone,

I want to know proper way to store the new custom CSS file for master page in shareopint. Because there are two way to store the location - 1. http://site/Style Library/filename.css from Sharepoint View allsitecontent  and 2. /_layouts/1033/styles/filename.css" . So Shoud I store under Style Library from sharepoint site or _layout/1033/styles/?

Thanks.