The Shiny Scizor has better IV's, but it can be possible that it is a hack (31's across the board). If I were you, I would probably take the other Scizor.
I believe the trade at first was the Scizor for the Heracross. Then you said you wanted the Gyarados, and then you went from that to the shiny Scizor and the Metagross, so you tell me what the trade actually is.