magicarp dilemma

One magicarp has level 25, the other has level 30.

As magicarp has really low stats, IVs have a huge impact on CP.
As gyarados has really high stats, IVs have a comparabely small impact on CP.

I think its because of the level difference. The first Carp is lvl 25, and the second one is 30.

It is because of the difference in levels. The first one is level 25 now. If you levelled it up to level 30 it would become a 181 magicarp, and evolved it would then be a CP 2772 Gyarados. So the first one is better but it would cost you another 38 candies and 44000 stardust to get it to level 30.