Using this free HTML Table of Contents Generator, anyone can create HTML CSS based table of contents for Blogger blog, WordPress blog or any online HTML based content.
Table of content Plugin gives same functionality but it creates dependency. User need to depend on third party code and plugin. If plugin not update time to time by developer, it can create issue for your site.
While in TOC generator, it gives pure HTML and CSS code which you can add to your content. This code permanently added to your post. TOC work same in all cases, as it is exist in post and not dynamically plugin generatet every time.
No doubt, it will take some more time at creation time, but, in future your post and site have no dependency. Also if you using some JavaScript based solution, it generate TOC dynamic, which not gives full benefit of on page SEO.
At the end, you can use your most suitable option for TOC. Main suggested point here is to use TOC in your content.