This post is in the wrong forum section. This section is for A7 engine only. But I guess a moderator will move it later to tools where competitive products are allowed to be mentioned.
There are a lot of differences between both. I try to write some of them down:
Source Code: You don't get source code for A7 but you get C4 source code.
Indoor: A7 comes with an ABT scene management. This is good for outdoor but does not help much with indoor sceneries. The pro edition supports BSP for indoor. But I did not see an A7 project using it in bigger worlds so far.
C4 has portals for efficient indoor scene management to render only visible geometry and lights on screen. So it can handle big indoor worlds better. You can use many more shaders, lights and shadows this way.
Outdoor: A7 has height map terrain. You need shader materials for multi-texturing. A real-time terrain editor is missing.
C4 will get a real-time terrain editor with endless voxel based terrain in next release. So it will allow you even to create steep hills and caves. And it uses background streaming from disc, gpu memory and RAM. But this is not finished yet.
Materials / Shaders:
A7 is open to add your own shaders and materials but does not have a real-time feedback material editor.
C4 comes with a nice material editor and allows to see all changes in real-time for things like normal, parallax, environment mapping and much more.
Coding:
Gamestudio uses a C-like scripting language and you can program via SDK in C++ or Delphi.
C4 needs good skills in C++ and provides a graphical node-based scripting editor very similar to Kismet (the scripting editor from Unreal Engine). Some users even created Poker games with this scripting editor.
Import:
A7 reads a lot of formats like 3ds, obj, fbx, tga, pcx, bmp. Only fbx can read animations. It has some minor issues here and there with different import formats.
C4 reads only DAE (collada, with animations) for meshes and TGA for images.
Shadows and Lights:
A7 uses stencil shadows for dynamic lights and static baked shadows for level geometry made in WED. C4 knows much more lights (point, spot, parallel, directional lights) and shadows (dynamic and static) and it gets new real-time shadow mapping with next update.
Optimization / Render Speed:
A7 renders small worlds fast enough. As far as I experienced the speed with lots of entities in big worlds need some better scene management. Shadows are not optimized.
C4 uses good scene management if you place enough portals. It can use some optimizations like static flag for stencils (it renders the stencil buffer only if necessary and not every frame) and much more. Shadows are tested if they are visible or if they reach into a portal.
In C4 you can constrain the distribution of fog, light, sound or shadows with cubes to certain areas. This helps to render only what you have to render in a certain area and block lights or sounds to get into neighbor areas.
Support:
C4 support is the best support of all indie engines. You get replies very fast and even the developer helps frequently.
Prices are both affordable.
License:
You need to spend money for a new license for every new major upgrade of Gamestudio.
C4 licenses are for a life-time. You get all updates / upgrades for free.
Summary:
At the end C4 is more professional and offers more options but it also is more comprehensive / sophisticated and needs more learning and good programming skills. A7 can be the better tool for a total beginner with the option to switch later to another engine. But A7 can also create nice (but smaller) games even in a commercial way. Especially for smaller casual game projects you could choose it.
