Need a second opinion on either walking my Gyarados or Larvitar...

I just evolved my 96% IV 149CP Magikarp to 2239CP Gyarados with Bite/Hydro Pump, but now don't have any candies to continue to power him up. It usually takes some time for me to catch Magikarp because they are not very local to my area so my only secure means of candies is via walking.

On the other hand, I just caught my first Larvitar this past week and was thinking about maybe starting the long walking grind with him since he's 5k/candy. Only problem is he currently has shitty IVs and very low CP so I wouldn't evolve him, and would pretty much be forced to wait to catch a better one or hatch one from a 10k and would have to be +90% IV before me to consider evolving.

Any thoughts? I'm pretty divided between the 2.

EDIT: Looks like it's pretty undivided in terms of opinions, so I'm going to walk the Larvitar. Thanks for everyone's advice.