With a blog you can advertise whatever you want to, and the same is true of a website. However, you are more likely to make a direct purchase from a website, and to seek information from a blog. Hence, the traffic you get on a blog are information seekers and those on your website may also be looking for info, but might also be wanting to make a purchase. So right away we can kind of separate blog readers from website visitors.
However, to return to the question: what is better, blog traffic or SEO traffic, as long as each is free it doesn’t really matter I would have thought. I suppose that it could be argued that the SEO traffic is more focussed because they have used your specific keywords to get to the page they landed on ,and blog traffic could come from ezines and other sources that are perhaps not specific to any product you are selling. Me, I would accept any traffic no matter where it came from, and quite frankly once the traffic gets to your webpage it is up to you to convert it to sales.