Gyarados with good iv or shadow gyarados with bad iv?

I almost have 400 candy to evolve this magikarp, I just got a shadow magikarp but the ivs are much worse.

According to https://db.pokemongohub.net/pokemon-list/best-per-type/water, the shadow version is better (#12 vs #29) bit what about the difference in iv? Which is better to invest in? Should I use a charge tm on the shadow guy? I won't be likely be able to get the rest of the candy by Sunday, will that still work?

Thanks