Feraligatr: Is HP worth?

As you probably will not power it up (vap is far better attacker/defender) and use him as a prestiger I'd go for the first one.

Actually, STA is the IV that will have the highest impact in feraligatr's performance, since it's his lowest base stat (170), but ATK is the stat that will have the highest impact on his CP. Having said that, since I draw the line in 82+ IV's, I'd discard the first one, maybe leave him as a prestieger, honestly I wouldn't power the second one up either, as IIt's simply a "bad vaporeon" and as an attacker, it doesn't need the boost, as you'd only use him in favorable matchups.

The second one seems so much more balanced.
between the two, I'd evolve the second one.

Second one is better in both max CP and actual combat ability.

Even if you don't care about it's max CP which is pretty low, extra stamina is guaranteed to make a difference in combat while the difference in attack or defence is not, plus the difference in stamina between these two is larger than the difference in attack.

0 and 15 attack already makes next to no difference, the difference between 12 and 15 is going to be even smaller. Same with defence. You're probably looking at like 1-2 more damage per usage of a charge move.

While having 8 more HP (at level 30) will make a difference in combat in terms of damage dealt, especially if you dodge. That will result in several extra Water Guns before fainting which will do more than a few points of extra damage onto your charge move.

I don't like unbalanced mons. And Sta is the most important stat unless it's Blissey.