Gyarados. Lots of people just look at that 4x weakness to electric and think, "That thing is crap, why would you use it?". I don't look at its weakness as a problem, in fact as long as you have a ground type those electrics will be useless. Honestly Gyarados has a decent movepool, good stats in almost everything, and it evolves fairly early depending on when you caught your magikarp, which for me is usually around lvl. 10-15.