For an imperial merian Aquamancer, which would boost damage more - Knowledge or War?

War. You're not gonna get all that much of a boost from +1 INT when you're already at 18

Knowledge is +2, by the way. Does that change anything?

I've often wondered this myself. I think if you're just after a straight damage boost, Kial's probably right - you won't see much increase with INT since for an imperial merian it's already high. But +1 to INT gives you other advantages as well, like longer demesne effects, and a boost to total willpower, which can help if you tend to burn out a lot while hunting.

EDIT: it's +2 buff to Int, which will probably only give you +1 to the stat. (Have a look at HELP BUFFS)

There are many abilities, spells and skills that help you increase your
attributes (strength, intelligence, etc.). These are known as "buffs".
Buffs are not calculated in a 1:1 manner, but rather are a weight that
is used to calculate the attributes. (This includes divine favours.)

Attribute Increase / Buff Weight Needed
+1 1
+2 2-3
+3 4-5
+4 6-7
+5 8+

NOTE: The exception is SIZE, which increases are calculated 1:1.


+2 from knowledge = 2 int unless you have buffs prior to that.