I think both are necesarry for site seo. Onpage is just like primary and offpage is secondary. For example you have to passed matric for doing your intermediate.
Both are very effective in SEO because you can't skip or choose one service between them
I think you should do both. Both are important.
Both SEO techniques are required to improve the overall ranking for the site. On-page SEO can give you instant result but to stable that ranking you have to do off page SEO (Link building.)
Thanks
The tendance of google is on-page more than off-page '' few links with high quality are important''
Both On-Page and Off-Page SEO are important and necessary.
Whats the difference between On-page and Off-page?
On-page SEO is what you do on your site.
Off-page SEO is what you do on other sites.
On-page SEO falls into two main categories: basic on-page SEO and In-depth on-page SEO
Basic on-page SEO implies that you use your keyword in
* URL
* Title
* Headline
* Page Copy
* Image Alt Tag
* Meta Data
In-depth on-page SEO deals with things like making sure that you don't have broken links, title and meta data issue. your URL structure is proper, and you don't have too heavy images.
Off-page SEO is all about building links that point back to your site. As a matter of fact, there are a lot of off-page SEO methods. Some of them are
* Blog Commenting
* Web 2.0 Properties
* Forum Posting
* Guest Posting
So, what is the priority? On-page or off-page SEO. Both On-page and Off-page SEO are extremely important in nowadays SEO, but you better focus on backings ( off-page SEO) if you're forced to choose just one.