SEO value of expired Pages

[razasaeed]

We run a classified site and after every day there are thousands of ads/pages that get expired which has no use to visitors. What is the best practice to deal with them keeping SEO factor in mind?

Should we keep them as they are linking to home page. redirect 301 to existing, 404 to home page or any other practice. Please advise.

[SEM-Freak]

301 them to the parent page in that category