Correct way of using logo in HTML5

What's the valid way of placing logo in a website.

<a href="#" class="logo"></a>

and CSS

a.logo
{
    display: block;
    background-color: transparent;
    background-image: url("images/logo.png");
    background-position: center center;
    background-repeat: no-repeat;
    width: auto;
    height: auto;
}

OR

<a href="#"><img src="images/logo.png"></a>