<iframe> or <object> - What should I use?

I need help evaluating the best tag to use between <iframe> and <object>. My use case is as follows -

1. Create an embeddable widget that users can customize on my application (change style, text etc.)
2. Allow users to embed the widget on their websites.
3. Make the widget responsive.
4. Lazy loading would be awesome.

I'm new to both iframe and object tags and reaching about them as much as I can. I'm still confused which one is the best pick for my use case.

The only down-side with <iframe> seems to be that it's not responsive. I'll really appreciate if you could help me make the right choice.

Thank you for your time. I look forward to receiving your responses and feedback. If there's another tag that can achieve this; please let me know.