Something I think really needs to be noted here is that any channel for marketing is really just dependent on your audience. If you've got a brand new product or service with no actual relevant search volume (except for maybe some long-tails), you probably need to do demand generation in other ways and SEO is less important. In other markets, PPC might be worthless or prohibitively expensive.
In general, always make sure your site is optimized as per best practice though.