[fieryshadowcard]

Pouch is technically the strongest physical skill in a Sense Type's arsenal. Emphasis on technically.

Here are the formulas at mastery:

Shuriken Master
[Throw AP/20 + DA]*33 (not factoring in Precise Pitch)

Pouch of Pain
66% of your filled WT. (example, let's say you have 8000 max WT, but you only have 6000 of that WT used up. PoP would deal 4000 damage. Of course, a Sense Type will have a crapload more WT than that.)

But, since this question sounds more like a "Which skill should I get?" question, I'm going to say this bluntly: Get Shuriken.