Answer
The B-O bond is more polar.
For B-O: Boron receives the partial positive charge, and oxygen receives the partial negative one.
For P-S: Phosphorus receives the partial positive charge, and sulfur receives the partial negative one.
Work Step by Step
According to the picture 6.8 (Page 263), the difference between the electronegativity of the boron and the oxygen (3.4 - 1.9 = 1.5) is greater than the same for sulfur and phosphorus (2.3 - 2.0 = 0.3).
Since that difference is proportional to the polarity of the bond, the B-O will be the more polar one.
For B-O: The less electronegative one is the boron, so it will be the partial positive atom, and the oxygen will be the partial negative.
For P-S: The less electronegative one is the phosphorus, so it will be the partial positive atom, and the sulfur will be the partial negative.
