Undrestand that high competition in advertising could very well mean heavy competition in seo also. Use the seodev niche market finder to enter your keywords and see which one will be the easiest to rank for before beginning an article for the best results. It's wrong to frame it as an "either/or" choice. Go for both.
Undrestand that high competitors in advertising could very well mean large competitors in seo also. Use the seodev specialized market locater to get in search phrases and see which one will be the most convenient to position for before beginning an article for the best results.
No one method can guarantee success in this range. But most helpful is content managing, I guess. Also, try to find competitive advantage in comparison with contestants