Answer
With slits, the fringe pattern is clearer and brighter.
Work Step by Step
As we can see by contrasting Figures 29.15 and 29.16, with slits, the pattern consists of long, parallel bars of light, rather than the less-regular, more complex fringes caused by overlapping circles of light waves passing through 2 pinholes.
Also, using slits allows more light to pass through, making the pattern brighter.