If you ask me I would say get the V3, more accessories, more bang for your buck.
From what I have gleaned, most prefer the original, as it is closer to the Robo they prefer, which is from the Robocop 1 film. So V1 or V2 is the go. V3 is from the Robocop 3 film. V3 looks less like Peter Weller than the other two. V3 has a different paint scheme. V3 has the detail of the back of his head, another plus.
I felt ripped off by V1, because Hot Toys chose to milk us with each additional release. I think Robocop was the first time they chose to use this methodical approach to releases. It has now spread to Aliens, Predators, Prison Breakers and Pirates