When Magikarp evolves into Gyarados it's Attack becomes way higher than special attack, personally I'd evolve the one with the adamant nature (also perfect for Gyarados imo)

i keep saying "dhs is only 24 years old" because i need you to take that fact under your jacket and keep it warm and peeping like a baby bird. it's only 24 years old! it's yet another thing inflicted us by the bush administration post-9/11!