Short answer: it depends. /blog is better if you just want more pagerank for your main domain, subdomain is better if you want to build your blog into somethin

Short answer: it depends. /blog is better if you just want more pagerank for your main domain, subdomain is better if you want to build your blog into something important on its own. A subdomain blog with good pagerank also gives you the ability to add heavyweight links to content on your main domain when you'd like to drive traffic to specific areas.