Waver or King Hassan at NP2.

Hassan he’s limited while waver is not so he can spook you at any time

I'd say go for waver, new servant>np 2 usually, its unlikely waver will spook you so its not worth counting on, and he will make farming a lot easier for you and in general he's a top tier servant who's always going to be relevant plus with him you will have a lot more team comps available to you, so unless Hassans your absolute favorite go for Waver

Waver

I think if you want to have KH solo meme, then NP>2 are suggested.

NP2 Waver is also good, but that "good" is like-absolutely all servants's NP level are suggested to have higher. His NP2-5 is more beneficial for 1 np shot team (like dual Waver+Shishou), or Art team.