To be honest all of them look very human. It should be safe to assume that intelligent life developing independently on another world would not come up with such humanoid shapes almost identical to humans.
That could be answer different ways.
Perhaps the outcome of evolution on planets that can support life leads to some kind of humanoid. Although it depends on how much different this planets can be.
Other would be to have sex with many different characters, the must work similar. I can't see that our MC could have sex with eg. Jabba the Hutt.
And also from a psychologic view, it is easer to put onself in the postion of other if they share similarity. A green humanoid alien share a lot more than with human than a slug type one.
But other concepts might have been even better. Since green skin and humanoid shapes are the constant, a dryad-like design would have been great.
Depend on what models you can get. I assume it is more easier to obtain humanoid aliens than some completely different looking ones (or too "only" change the skin colour....)