There has been some confusion in the community around Unity’s versions and which ones should be used.
(If you’d rather watch a video, you can see it at the bottom of this post).
There are two streams – the Long Term Support or LTS stream and the TECH stream.
When you need a stable environment that won’t change for two years, except for security fixes or major issues that affect a lot of people, you want to go with the LTS stream. This can be thought of as the last released minor version of a major version of Unity. For example, Unity 2017.4 is the LTS version of Unity 2017.
When you want to work with the latest features that Unity has to offer, you want to take advantage of the TECH stream. Currently, the Unity 2018 version is in the TECH stream.
In general, if you are doing new development, you most likely want to be utilizing the TECH stream. If you release your game, app, or experience using Unity 2018.2, for example, then you will want to update your code once 2018.4 LTS is released. That way you can be on the latest stable version that has long term support. You will effectively move from the TECH stream to the LTS stream.
If you are doing active development for additional content, or whatever, you could choose to stay on the TECH stream and upgrade your project to the latest version of Unity, which in this example would be Unity 2019.1 (which would be released at about the same time as Unity 2018.4 LTS).
There is a great image that Unity has that shows how this works.
Here’s a video where I talk about this some more: