With both of them, I suggest a more high tech looking background. Or, failing that, go simple and plain. You can hide the horizon with a vertical ground plane (just add a ground plane and rotate it 90 degrees)..
The 'bots look like they are floating. Maybe a optical illusion because of the very dark shadows? If they are floating, they should be lower. Otherwise go to the sky lab and soften the shadows slightly (change the shadow color) Their pose is rather stiff. Maybe reposition them slightly? Or keep them nice and stiff, but show them in storage?
The walker image seems a bit unbalanced. It is on an all white plane without shadows... but the sky is still present.