Source vs Armory3D

Valve's official documentation website is great for newbies. It demonstrates the pros and cons of the engine (and since the website isn't maintained by Valve, but instead the community, the pros and cons are largely unbiased). There are also a number of pages dedicated to entities used within official Valve games and also community-made mods that were turned into full-fledged games by Valve. These pages explain the ins and outs of how most source programming works. There are also guides for Valve's tools which are both included in Source SDK and in any Valve-developed game.

Since it has precalculated lighting, this engine is great for low end PCs too.

You don't need to code your own door or ladder etc. You can pretty much use every entity used in Half-Life 2 yourself easily.

Of course you can program stuff into source but for level design only, source has a really easy input/output system for your level logic (e.g. doors, trigger when player walks into room...).

Source includes Source Filmmaker, a video capture and editing application.

Does everything in the same application. No exporting-importing assets, make a cube, hit run, cube appears, make a character, hit run, the character appears!

Physically based
Cycles material nodes
Voxel-based global illumination
Temporal anti-aliasing
Tessellated displacement
Screen-space raymarching
HDR pipeline

Export to all platform that Kha supports.

Although the is an obvious lake of community help, it is still there if you look on the Armory forum or there discord your sure to find help for any problem you have.

Although Armory has been a little slow in the development, tutorials on YouTube are being released almost daily and the documentation is also being updated regularly.