For the size holes you are talking about for sheathed electrical cable, the size of the hole is not that critical. Locate the holes above the centerline of the joists to minimize the effects of horizontal shear stresses, but not so close to the top to expose the wires to the possibility of nails or screws being driven through the top flooring into the wiring. If the joists are 2x8, limit the size to 1 inch. If they are 2x10, limit the size to 1.5 inch. If the holes are going to be near the ends of the joists, (near the support points) the holes could be much larger. Whatever you do, keep it neat. There is nothing worse than going into a basement and seeing electric cables running in all directions and diagional.