for me, who earlier made only tiny 2D games in Delphi and Java, it was much easier to start with 3dgs. earlier I worked for a few years as a CAD/CAM engineer, so the editors interface was also easy and clear. (normally it's easy for me to get familiar with unknown editors without tutorials, except Blender and DAZ Studio)

I found unity editor too complex and "too user friendly", did not know what are those hundreds of options, what I have to set and what can I ignore. making a new small project in unity is too complicated, a bit messy, and requires huge disk space, because of importing those packages, comparing to 3dgs where I can clearly use a few files only, and I'm not forced to organize my stuff by an editor, only simply in Total Commander and in my scripts. and I've ever wanted to write 100% own codes, not to use ready made scripts what I don't know deeply, e.g. for camera and character handling. in the other hand, if you don't want to program, only do some level design, and your game has no special game features, you can get a lot of resources for unity for free or for money, it is also a walkable way, but this is not my way.

okay now I'm more experienced, I can handle unity editor, and know most of the available options are what for, or where I can find the info, and I see unity's system is much more up-to-date and more advanced, but for my taste I can organize my work better in 3dgs than in unity, and currently I have in 3dgs what I need.

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but what is more important, for me unity pro is too expensive, and the free edition does not offer: LOD, dynamic shadows, terrain lightmapping, water reflections, hdr. and these are needed for me, and get by 3dgs commercial whose price is acceptable.

moreover, in future I would not move to unity, I would choose rather Esenthel (it can be okay for one person development) or maybe UDK (but this would really require a developer team), depending on my project requirement.