DE's

When someone asks about an operating system on Linux what they're typically referring to is the Desktop Environment. To Windows or Mac users this may seem strange because to them the operating system is most noticeably changed by the theming and visual attributes of the system they're working in. But on Linux the distro is actually just the design philosophy and application set that you interface with.

What beginners actually typically complain about isn't the distro but rather the way their computer looks, and this is determined by the DE.

The desktop environment matters so much because it dictates the feel of everything outside of the technical. What you can theme and the default general look and feel of the OS is actually dictated by the DE and in this respect there are multiple options but there are two that stand-out for their polish and sleekness most.

Gnome

Gnome is the most bundled DE by far and though often believed to be the first actually isn”t. It is modern, it is sophisticated, and it is comprehensive but it is opinionated. Meaning that it intentionally restricts and actively tries to deter customization. This doesn't make it impossible but it requires more work than it's major competitor KDE Plasma and it often drives away those moving from Windows because it's interface is actually heavily inspired by MacOS. That being said, if this style appeals to you then it is probably the most polished desktop environment that exists and it's developers update it near constantly.

KDE Plasma

KDE Plasma is the first DE ever made for Linux and was avoided for a long-time on the basis that it was slow and buggy. These issues no longer persist and today KDE has begun to be used for things like SteamOS and is rapidly growing in popularity as it closely mimics Windows, is thoroughly customizable, and often is on the frontier of new features.

Cosmic

Cosmic is a project that was started by System76 for their PopOS distro and while initially starting as a heavily skinned Gnome fork eventually became an entirely original DE with it's own standards and apps. It's extremely lightweight, fast, and looks gorgeous but it is much newer and so any deciding whether to use it will have to be mindful of potential bugs, missing features, and lack of icons or native applications.