Ok, I'm going to compare the two.
- Base 95 Special Attack (Walrein)
- Base 110 Special Attack (Vaporeon)
A win for Vaporeon
- 130/60/95 (Vaporeon)
- 110/90/90 (Walrein)
Since HP matters more in my opinion, as well as a higher special defense stat, a win for Vaporeon
Win for Vaporeon, jk, a tie
- Vaporeon has Ice beam, Shadow ball, Hyper voice and Signal beam
- Walrein has Signal beam lmao
Win for Vaporeon
So, I would say to use Vaporeon.