Which Magikarp is better to evolve?
Karp 1: 93% 14/13/14
Karp 2: 91% 15/14/12
On average the 93% will be better. There will be a few levels where the 91% hits a breakpoint and performs better. This is the reason behind the community-wide obsession with 15 attack. You can always* power up your 93% one more time to hit that same breakpoint and you get slightly more bulk.
*There is a very slight risk that at some point Gyarados will find a matchup where it only hits a breakpoint at level 40 with a 15 attack.