You can not leave any of the two both of them are very important in SEO of any site. They work hand in hand...
Both are important in SEO, without onsite optimization your onsite optimization have no value, or if you do onsite optimization or you are not doing off site than there will be no benefit in seo. First you need to optimize on site than offsite.
See friend, both methods is very important for SEO. While starting your website On page is more important but when site is old then Of page SEO works. But OF page SEO is a regular process but OF page is one time process.
Hi Dear, Both are very Important for any site. Because if On Page is better then you can get good ranking on your site. And after On page you can doing Off page so. Both are very very important.
Personally I think all aspects of SEO are equally as important. It's like saying cream is better than milk in your coffee Take care of all SEO on your website. I think there may be instances where some SEO should be taken care of more than others, I am NOT an SEO expert I am still learning so anyone can feel free to correct me, I do feel however that if you leave a hole somewhere in your efforts for example in off-site seo then you will not reap the rewards
on page and off page both are related to each other they workas body & soul. so both are impotant for seo.