For an overweight person, do you use light weight,more reps or heavy weight, few reps?

There shouldn’t be one answer for everyone. Everybody reacts a little different to a given stimuli. The goal is to FIND what works best for a given individual. Keeping track of a program and only changing 1 variable at a time (to determine if that variable change improves a programs results) is the key to constructing the solution to an individuals program needs.