Why not have an option to do either?

Pisces-Studios said:
So I can only have one.

But you need to decide this not only regarding some shading and post processing.
You have to decide already when creating the content itself.
The robot is cartoonish, the helicopter is realistic. This does not fuse well.

It took me some time to realize that's the reason i could not answer the question.

Some minor tips:
Rotate the tower 45 or 30 degrees, so there are no alignment issues creating unwanted Moire effects of geometry.
Too much black overall - indicating night, conflicting with brightly lit up robots - indicating daylight. Such sunset is hard to get right with flat shaded boxes, so that would be an argument to make the robots more round / detailed, which would allow for lit silhouettes.
Too high variation on geometry features used for the robots. Bold, boxy bodies, but super thin guns. Make them big guns, so they become an actual threat already from visual expression.

The conclusion is that all your (programmer-) art issues come from unconscious use of very high contrast, regarding both shapes and colors.
High contrast must be used wisely, to guide the attention of the audience, which can only work if subtlety is used equally thoughtful.

The overall composition of the image is fine.
Just too much weight on the right side, because both the helicopter is right, and the ‘important’ robot is on the right too. I would compensate by putting heli on the left or moving the tower out of center to the left.

Now after staring at it for so long, i clearly prefer the CGI image. It feels less constructed, and projectiles look much better. Maybe some trees could burn on the left.

Edit: Watched your blog video from the alpha. Does not look bad at all.
But imo the robots really lack some detail, as said above. The rest is consistent, it's just the robots which are surely worth some work.