When comparing Source vs Panda3D, the Slant community recommends Panda3D for most people. In the question“What are the best 3D game engines?” Panda3D is ranked 4th while Source is ranked 29th. The most important reason people chose Panda3D is:
The liberal license allows use of the engine for any purpose without restrictions or royalties.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Great documentation
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.
Pro Runs on every potato pc
Since it has precalculated lighting, this engine is great for low end PCs too.
Pro Many basic entities
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.
Pro Visual logic, no programming
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...).
Pro Has a built-in video capture and editing application
Source includes Source Filmmaker, a video capture and editing application.
Pro Easy way to export or load source models to unity and maps
Pro Free, open-source, and permissive license
The liberal license allows use of the engine for any purpose without restrictions or royalties.
Pro Will be very easy for developers already familiar with Python
Although it's possible to use only C++ to program in Panda3D, all its power is available to the Python scripting language, while not trading in performance since the performance-critical parts are implemented in C++.
It has a powerful binding layer that exposes the vast majority of the API via Python-based interfaces.
Pro Supports most popular physics engines
Panda3D has in-depth integration with industry standard physics engines such as Bullet, NVIDIA PhysX and ODE, but also offers a simpler built-in physics engines that will cover more basic needs.
Pro Flexible scene and object hierarchy system
Creating weird world constructs is generally a breeze. The node system the engine runs with allows to build self-looping worlds and, on large scale, non-Euclidean scenes without having to introduce a huge amount of custom code.
Pro Powerful profiling and debugging tools
Panda3D has a suite of powerful tools to help track down performance bottlenecks, memory leaks and examine internal state.
Pro Supports browser deployment
Panda3D offers web plug-ins that allow deployment of an application to all major browsers. A WebGL port is in the works as well.
Cons
Con Only for mods
Normally, you can only use the Source Engine to develop "source-mods" (as Steam calls them), however the developer wiki is correct in saying Valve have a proven track-record for finding source-mods and turning them into fully-fledged games, Black Mesa Source is a good example of this, as it began life as a source-mod available for free, however Valve turned it into a fully-fledged and paid game.
Con SDK is outdated and difficult to use
Source SDK has not been updated in ages, and has instead been "re-released" under different names, e.g "Source SDK 2013 Singleplayer".
It's honestly easier to use the version of SDK included with any Source game, namely Portal 2 or DOTA 2, since both have a variant of Source SDK that is more updated than anything you can find in the tools section of Steam.
Con No unified editing program
Unlike Unity and Unreal, Panda3D doesn't currently offer a single, unified editing program in which objects can simply be dragged in and assigned properties (although third-party solutions are available). Developers are expected to design their scenes in a modelling program like Maya or Blender instead, and import them into Panda3D using Python code.
Con Limited tutorial
Step by step tutorial is limited. Manual is too general and short without examples. Samples are too complex for beginners.
Con Direct3D support is behind
Direct3D support not up to par with OpenGL support, only version 9 is supported.
Con Terrible compilers support
Does not support any other compilers then MSVC on Windows, neither Clang nor MinGW.
Con Developer isn't very competent
Panda3D only has one developer and he utterly fails to fix problems with his engine, instead focuses on style guidelines and breaking code.
Con Loading Pandas3d will change your builtins to contain non explicit references to non-standard helper functions
A lot of the pollution comes from storing global state. Instead, you can store and update the global state of a namespace instead. As for the built-in pollution, you can make a wrapper that backs up builtins, imports pandas and then restores builtins, though this may not work as pandas almost certainly uses it's extra builtins to work. The best thing to do would be to explicitly import the same objects that are in the builtins over the top of the modified builtin namespace, although it doesn't remove the code smell, it helps to make things look less (if not at all) magic.