I’ve been developing sites with Joomla for many years and have experience with many extensions. Here are some of the essential ones I use on almost every site.
Akeeba Backup
Akeeba Backup is the first result you’ll see on the Joomla Extension Directory’s Top Rated page, and for good reason. This extension makes it incredibly easy to backup and migrate your Joomla! powered websites without the need to rely on proprietary or paid services provided by your web host. There’s no need to manually download thousands of files or export the SQL database.
Install the extension, run a backup, and download the backup file to a safe location.
The single file backup contains everything from your website, including the database. It can then be restored to any web server using a simple script that auto-configures the site to work with the new host (you just have to plug in the new database info).

You can schedule backups if you purchase the paid version. However, the free version allows an unlimited amount of manual backups at any time.
Convert Forms
Convert Forms is a free form builder with paid extra features. I like this extension a lot because the free version still has all the basic features you’d need for most websites including email notifications and saving form entries to the database. The interface is very approachable and easy to use.
I’m currently using this extension for building forms on this website!
I love how they don’t require a backlink to their site, even in the free version. If you’re a developer, it’s easy to style forms and add custom CSS if needed.

JCE
Joomla Content Editor (JCE) is an alternative WYSIWYG editor for Joomla that’s been around for a long time. Some of its more powerful features include layout tools, templates, and an enhanced media manager.
The free version has a ton of features and the paid version introduces even more useful plugins. You can assign different profiles to different user groups just like with the default Tiny MCE editor.
That said, as someone who does most of my article writing in code view, I don’t find all of it’s features very useful. It can, at times, produce bloated articles. With so many features, it can be overwhelming to configure.

I would say the best use case for this editor is in scenarios where you have multiple authors working on content and want them to be able to easily produce consistent layouts and styles.
If most of your articles are mostly text and don’t require extensive styling, you probably won’t notice much benefit using this over TinyMCE.
TAGZ Open Graph
TAGZ Open Graph by Roosterz.nl is essential if you want to optimize your content to appear on Facebook or Twitter. Joomla includes basic SEO features and metadata, but it does not include support for Facebook or Twitter metadata. This means when users share your articles on Facebook or Twitter, the platforms are guessing what to content to show.
For example, suppose a user is trying to share an article you wrote on Facebook. Your site is called “LovelyPets.com” and it includes information about caring for animals. The article is about selecting a groomer for a dog and it includes an image of a dog at the groomers.

If left to its own devices, Facebook might load the wrong information from the page. The user is trying to share the article, not the website.

TAGZ can preload content from an article, like the intro image or some text from the description. It adds this information as metadata to the page using Facebook’s Open Graph format. This means you can control what is displayed when people share a page on Facebook or Twitter! This results in a better use experience, and can lead to more users visiting your website. The preview of the article on the right is much more relevant than the generic listing on the left.
The free version can handle all the basic tasks, though you have to remember to manually save the OG data for each article you create. If you want a more automated solution, you can get the paid version.