H1 vs H2 vs Other for website title/logo and SEO

I usually don't put the logo or site title in an H1. The way I like to look at it is that each page is a document. That document is about a particular subject, as reflected in the page title and also the main heading. The website itself is just the publisher of the document. So, semantically, it's incorrect to use the site logo or name as the main heading of each page. Logos are displayed prominently to remind the user where they are and for branding purposes, but they're not actually part of the content or document.

I mean, when you watch a news story you might see a little news channel logo in the corner, but the news story isn't going to be titled "CNN" or "BBC News". The headline will be about the story, not the network publishing the story. Likewise, when you read a magazine, only the article title is used in the heading, not the name of the publication.

It's also semantically incorrect to use an H1 tag for the logo/site name and one for the document title. Headings define the hierarchical structure of the content on the page; using one for the site name and another for the document title is like saying, this page has 2 main sections: "mydomain.com" and "contact us".

See Page #37 of Google's SEO Report Card document:

Most product main pages have an opportunity to use one <h1> tag, like the example above, but they're currently only using other heading tags (<h3> in this case) or larger font styling. While styling your text so it appears larger might achieve the same visual presentation, it does not provide the same semantic meaning to the search engine that an <h1> tag does. The product's name and/or a few words about its features are great to have in an <h1> tag for the product main page.

Per Google's own analysis of its offerings, I would arrive at the conclusion that Google expects a unique, page-specific value to appear in an H1 (the illustration in the linked doc illustrates this).

Here is a good rationale: Your logo is an image, not a <h1>

Semantically, <h1> should be used for the page title, and the page title ought to be unique per page. Your logo or site name is not the page title (aside from perhaps the home page).

Your logo/site name should be in a plain div, perhaps with ID of 'heading'. Or, the <header> tag if using HTML5.