As an EK and someone who hunted Sea Serpents for a long time I feel confident to say: EXP PREY
Why is Loot Prey bad at Sea Serpent?
- Sea Serpent's loot is really bad and poor, that means that the bonus loot from the LOOT PREY will also be bad and poor. What would the extra loot be? At Sea Serpents, probably just extra gps, pots, a plate legs, etc... not worth at all.
- Loot Prey: 40% chance of getting extra loot
Why is Experience Prey good at Sea Serpents?
- Their Exp is pretty decent: 2,300 exp on 100%, meaning that with EXP PREY, you will get 3,220 exp per Sea Serpent, extra 920 exp per creature, on 100% stamina.
- Exp Prey: works on 100% of the Sea Serpents
So, experience prey is much more valuable at Sea Serpents than Loot prey.
PS: damage prey would also be very good, because they are already weaker to physical, meaning the EK would deal a lot of extra damage with damage prey, which would increase EXP / LOOT. :)