Best SEO practices for mobile URLs: 301, rel=canonical, or something else?

Question

I am developing a site with a mobile version and am trying to figure the appropriate way to manage the URLs for search engines. So far I've considered:

1. Having a separate mobile site (m.example.com) with rel="canonical" links to the regular site.
2. Putting both the mobile site and full site on one URL (example.com), and doing user agent sniffing.
3. Another opinion:

Spencer: "If you have a mobile site at a separate location or URL, you should 301 redirect each and every mobile page to its corresponding page on your main website. Employ user agent detection so that the mobile optimized version is served up if someone's coming in from a hand-held. - http://developer.practicalecommerce.com/articles/1722-Mobile-site-Development-Best-Practices-for-SEO-Usability

Both 2 and 3 make it hard for a user who wants to switch to the full site or mobile site manually, but I'm not sure 1 is the best alternative.

What's the best way to write URLs for a mobile site?

Answer 1

I know this question is old, but Google now provides better guidelines on how to develop website for Desktop and Smart Phones.

https://developers.google.com/webmasters/smartphone-sites/details

Answer 2

This recent blog post from Google might be helpful

Answer 3

This is an even older post now, but I recently implemented a mobile-specific sub-domain based on this advice from Google.

Google does not favor any particular URL format as long as they are all accessible for all Googlebot user-agents.

The important thing is that you signal to Google the relationship between the two sites so you don't get penalised for duplicate content. This means using tag with rel="canonical" and rel="alternate" elements and redirecting visitors based on user-agent strings.