Ubuntu is the most known Linux distribution owing to marketing and mainstreaming of Linux.
Most people from the earlier generations have used Ubuntu as their first distribution. Overall, it was easy to find on the Internet, easy to install, and it worked well on the widest available hardware. The tradeoff to this wide usability was the inclusion of non-free drivers and software. This means that Ubuntu was packaged with software that was not open source to allow more computers to work. Some have praised this strategy, others have condemned it.
Ubuntu has had other controversies as well, making it a distribution that people either loved or hated over the years. One of the early contentions was the inclusion of Amazon search results (leading to an affiliate link of products) when you searched in the OS menu bar. This even pre-dated Windows doing such Internet searches from the desktop. Many people were alienated by this approach because many people switched to Linux to avoid the shenanigans of Microsoft. In recent years, they have prioritized the Snap software distribution model, which many have rejected because of the proprietary distribution. Still, some praise it for a more secure and containerized application distribution method that does not reply as heavily on system dependencies. Both camps make good arguments.
As for the usability, Ubuntu is generally a very stable operating system with ease of use. The official build uses a highly modified Gnome desktop environment, but several official flavors are available that include the most popular desktop environments. These are maintained by separate teams, but with the authority by Canonical (the parent company of Ubuntu) to release the distributions under the Ubuntu name.