Once you have decided to build a site using the WordPress platform, the next step will be deciding whether to use WordPress.com or WordPress.org.
Flexibility of Your Site
The complexity of your site will help in deciding. If your site is going to be a simple personal site, WordPress.com may be better suited to your needs. If your site is going to be complex and require themes and plugins to add additional features, the better option will be WordPress.org. WordPress.org offers more flexibility than WordPress.com
Availability of WordPress.com and WordPress.org
Both are free; anyone can sign up on WordPress.com at no cost while the software for WordPress.org can be downloaded for free for use on your own server.
Below is a comparison of WordPress.com vs WordPress.org.