Source vs Leadwerks

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.

Good API tutoials, workshop elements which can be loaded from steam.

Has an acceptable 3D map editor that is easy to use.

Leadwerks's flowgraphs resemble flowcharts where each box represents a function or value, with connections between them representing program flow. This provides a better at-a-glance indication of game logic than a simple list of events, and makes complex behaviors easier to accomplish.

It makes game developing much easier if you have someone backing you up when you run into a bug or other issues, and get replies within hours .

Standard edition of Leadwerks costs 92,99€. Additionally, it often goes on sale on Steam.

The terrain editor allows sculpting, paint, vegetation placement and importing of external maps. Especially the painting is done very well and can lead quickly to very professional looking results.