The salt that its aqueous solubility most sensitive to pH would be calcium fluoride (CaF2). It is an insoluble salt which when reacted with an acid, it yields this equation:
CaF2 (s) + 2 HX (aq) → 2 HF (aq) + CaX2 (aq)
Since it produces H+ and and OH- when combined with water, it is therefore sensitive to pH.