Housetraining: back yard or pee pads?

Hi! I'm looking over the best ways to housetrain my baby, and I'm wondering what would be better: to train him to go outside, or on a peepad? See, right now it's summer, so I am home with him almost all day, but come Sptember, I'll be at school for 7 hours or so. We have a very large backyard, but because of the school issue [and nobody else will be home either] I wonder--would it be better, in your personal opinions, to yard or pad train him? Thanks in advance!