Answer
At the top. It's the same.
Work Step by Step
The baseball's horizontal velocity component stays the same throughout the flight. At the top of the flight, the baseball's vertical velocity component is zero. The Pythagorean theorem shows that the overall speed there will be a minimum.
The velocity at the top of the flight is the same as the horizontal component of velocity.
This is discussed on page 187, and shown in Figure 10.9.
