Since version 2.5 Blender is really great especially because of the new UI which makes it easier to use when you come from a different 3d modeling toolkit (I was rather used to Maya, 3DMax and Cinema4D).
And it’s source code is available for free… which seems also to be the killer argument for UE4 here!
Additionally, the scripting language is Python so you don’t need to learn anything new like MEL, COFFEE or something.
Alternatively you could use the free trueSpace but it has been abandoned by Microsoft after its purchase.