I bought the C4 engine one year ago. And I don't like it. The world editor is nice and the features are kicking some other engines away, but the tutorials and wikipages are mostly outdated. Instead of releasing more and more features, the c4 creator should focus on documentation and renewing the tutorials. And realy, the demos are helping no one if you want to do other things than see spheres jump up and down. So the c++ code is realy clean, but if you have to write pages of code only to init the engine and than additional pages to let some balls jump up and down, than this effort is not worth the result.
Neoaxis engine is nice. But not everyones taste. It is based on the ogre engine. I like how it handles light. I never red how it does things. But I had a scene with at least 30 dynamic lights in it. And the engine didn't slow down at all. THe editor is crap.