SEO alone is not going to take you far these days. Without a solid social media exposure and, yes, targeted PPC advertising your site may end up sitting dormant, even though you will have the best SEO possible. Basically, it boils down to these three things: Advertising, advertising, advertising.
SEO can convert good as well but in not verbal way. For example - you have consulting business and operate in local area. But becouse recommendation from other people you can convert high as well. It depend what are you doing!
ppc means more Advertisting $$$ SEO is Free and very good traffic if you rank for the right keyword, But it requires much work involved, link building, content creation etc but if you want to go that route you can find a couple of service on fiverr to help you out on this