depends on iv, your example is pretty biased, cuz 20+ all scizor is actually pretty ok and usable in PvP. If it's a 10- scizor that's not usable in PvP, I would definitely get the all 30+ scizor. Because 30+ in all iv is 1/13900000(not counting nature and ability), and a shiny is only 1/8200 approximate. However if it's PvP usable shiny vs. very very epic regular pokemon, I would take the shiny any day.