Css 用徽标图像替换 H1 文本：SEO 和可访问性的最佳方法

It seems like there are a few different techniques out there, so I was hoping to get a "definitive" answer on this...

On a website, it's common practice to create a logo that links to the homepage. I want to do the same, while best optimizing for search engines, screen readers, IE 6+, and browsers who have disabled CSS and/or images.

Example One: Doesn't use an h1 tag. Not as good for SEO, right?

<div id="logo">
    <a href="">
        <img src="logo.png" alt="Stack Overflow" />
    </a>
</div>

Example Two: Found this somewhere. The CSS seems a little hacky.

<h1 id="logo">
    <a href="">Stack Overflow</a>
</h1>

/* css */
#logo {
    padding: 70px 0 0 0;
    overflow: hidden;
    background-image: url("logo.png");
    background-repeat: no-repeat;
    height: 0px !important;
    height /**/:70px;
}

Example Three: Same HTML, different approach using text-indent. This is the "Phark" approach to image replacement.

<h1 id="logo">
    <a href="">Stack Overflow</a>
</h1>

/* css */
#logo {
    background: transparent url("logo.png") no-repeat scroll 0% 0%;
    width: 250px;
    height: 70px;
    text-indent: -3333px;
    border: 0;
    margin: 0;
}

#logo a {
    display: block;
    width: 280px; /* larger than actual image? */
    height: 120px;
    text-decoration: none;
    border: 0;
}

Example Four: The Leahy-Langridge-Jefferies method. Displays when images and/or css is turned off.

<h1 id="logo" class="logo">
    <a href="">Stack Overflow</a>
</h1>

/* css */
h1.logo {
    margin-top: 15px; /* for this particular site, set this as you like */
    position: relative; /* allows child element to be placed positioned wrt this one */
    overflow:hidden; /* don’t let content leak beyond the header - not needed as height of anchor will cover whole header */
    padding: 0; /* needed to counter the reset/default styles */
}

h1.logo a {
    position: absolute; /* defaults to top:0, left:0 and so these can be left out */
    height: 0; /* hiding text, prevent it peaking out */
    width: 100%; /* 686px; fill the parent element */
    background-position: left top;
    background-repeat: no-repeat;
}

h1#logo {
    height: 60px; /* height of replacement image */
}

h1#logo a {
    padding-top: 60px; /* height of the replacement image */
    background-image: url("logo.png"); /* the replacement image */
}

What method is the best for this sort of thing? Please provide html and css in your answer.