Should I use the span tag or the i tag for an icon?

I'm just curious about which one is better to use in order to add a custom icon next to my links.

<ul>
    <li><a href=""><i class="home"></i> Home</a></li>
    <li><a href=""><i class="downloads"></i> Downloads</a></li>
</ul>

or

<ul>
    <li><a href=""><span class="home"></span> Home</a></li>
    <li><a href=""><span class="downloads"></span> Downloads</a></li>
</ul>

Thanks.