Which one should you choose?
For most cases Javascript code is the best choice, but exceptions apply.
Javascript embed code style has several big advantages over the other options. This includes fullscreen mode on iOS devices (iPhone, iPad) and better performance with multiple embeds on one page. .
However, there are some CMS systems and publishing tools that do not accept 3rd party Javascript. This is why we offer the more traditional HTML solution. So, if the Javascript code doesn't work, try HTML. One good exmaple where you need to do this is when embedding a 360 image from Kuula on Tumblr.
If you use a platform that supports Embedly the you should grab the Embedly URL. Systems that support Embedly include Linkedin publications, Medium blog posts, Matterport hotspots and many others.
Finally there is the humble link. This option can be useful for developers who write their own embed management code in Javascript. You can use the link and set it as the src attribute for the iframe element in your app.