The main reason I attempting to use Unreal Engine is due to the inbuilt C++ support. I have used Godot before, and getting C++ to work with it is a pain, and there is also a lack of much updated documentation. (The most updated I found was from version 3.5).
I have since tried Unity, however I doubt I shall be returning, mainly due to the controversy the past CEO began. (IE, implementing a fee each time your project is downloaded), which, despite the changing of the CEO, it still shows what mindset the company is in, and solely creating my games with an engine controlled by that sort of company is not something I’d like to do. Also, the C++ support is pretty awful, as is the lack of documentation.
Source 2 has virtually no documentation, so I don’t believe I’d like to be touching it anytime soon.