All of them are grammatically correct, although the last is clumsy enough that I doubt you'll hear it.
Of the first three, the only difference between them is stylistic: how brief do you wish your sentences to be?
That said, the construction usually uses two words which are related, such as "I was a lawyer, but I was more like a secretary." These are related in the sense that both sorts commonly work in the same office, and an individual might serve either function. It is very difficult to connect clown/elephant: they are both found in a circus, but they are not (usually) considered interchangeable. Exactly how does a person behave so that he is more like an elephant than like a clown? Eating peanuts and blowing water through your nose doesn't count.
Likewise, a straw man is an imaginary opponent in an argument, selected to provide an easy, but erroneous, means of attacking a real opponents position. A spectre, while also (one hopes) imaginary, is not part of any argument technique that I'm familiar with.