Good guesses but you're so cold

 

Siege Megatron has no purple.

 

Classics Megs is the only one without a G2 recolor.

 

Siege Megatron didnt get (yet) a Takara specific repaint/redeco

 

Siege Megatron is te only one Released as a HasTak collaborative effort?

 

Siege Megatron is the only G1 based Megatron?

 

That one could be debated, as G2 and Classics are both direct fallow-ups to the G1 comics. With that line of thinking they are all "G1" based vertions of Megatron.

 

the clasics one is the only that turns into a gun

 

Fair.

 

That's another one you could call on a technicality. A tank is a model gun platform, while a revolver would not be considered a gun by the military.

 

Again all very good guesses but here's a hint, neither paint job or alt mode have anything to do with it

 

GDO Megatron has no arm cannon.

 

You got it

 

Alright, there are two correct answers. I'll take either one.

 

one them is not holding the gun on his right maybe

 

No it's a difference with the toys themselves, not how they are posed.

 

Megaplex is the only one without trim paint?

 

Maybe, but Megaplex is not in that picture.

 

Megatron doesn't have trim paint?  

 

Neither does Air Hunter.