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Reaction between sulfuric acid and ammonium hydroxide will give ammonium sulphate and water . Water is a weak electrolyte and less dissociated as  compare to NH₄OH  and H₂SO₄ .
2NH₄OH + H₂SO₄ ---> (NH4)2SO₄ + 2H₂O

During this reaction amount of ions on the reactant side is more than the ions on the product side. So when the reactant is getting converted into product, the number of ions are decreasing because of the formation of more water which is not a strong electrolyte. As the number of ions are decreasing the conductivity will also decrease with  more volume of ammonium hydroxide is added and more water is formed. But once the titration is over and amount of ammonium sulfate formed has become constant, there is no further increase in concentration of ions significantly. NH₄OH added is also weak electrolyte and not fully dissociated. It means conductivity becomes nearly constant.
Graph B is well fitted
Graph A is good for strong acid and strong base