I would say "the longer the better". Look for quality, unique content of up to 1000-1500+ words on home page and up to 600+ words for the internal pages you want to rank Avoid "thin content" pages with less than 200 words of unique content on them. Having too much of such pages on your site can lead to a domain-wide Google Panda penalty. Best to rewrite or to "noindex" such pages.