<body bgcolor=\"yellow\">
this uses bgcolor property of the body tag
<body style=\"background-color:yellow\">
uses the css to display background color.
Suppose you are working on a big project with some 100 pages in it. For such projects we write external css files and link it with every 100pages. You might know about what an external stylesheet is and how to link it in a page, if you have completed the CSS section of the tutorial. Now we only need to change one css file to change the background color of body, and it will affect every 100 pages.
So i think the first one with css is the better way.
Regards,
Sanjay S Nair
Sep 9, 2009