Definitely Godot Engine. One of the greatest and easiest Game Engines I have ever used! Lots of great features and there are getting more and more!

The inbuilt programming language GDScript is really awesome too! It's a custom language built extra for the Engine, which makes it super easy to use and integrate! The syntax is a bit like python but better.

Because it's not as old as unity or unreal engine, it's not as feature rich. But I think that's okay. It allows you to get used to the current existing features, and then heading on to the new ones.

What I really enjoy is that, just as in this community, you can just talk with the creators of the engine. Asking questions, suggesting features and discussing things! They'll answer nearly everything!

Not to mention the graphics! They are really good and are nearly able to compete against Unity!

There's also a visual language you can use. Just like Unreal Engine Blueprints! Never tried it tho...

The scenes system is very easy to understand. You basically have a lot of "components" which you can use in each of your scenes. This also allows for making simple extensions!

All in all, a great engine! If you are a game developer I can definitely recommend trying it out!