I like either 2" strips or 1.5" strips. The only time I would 2.5" strips would be for an uneven log cabin, in which case the narrow strips would be 1.5".
By cutting jelly roll strips in half, do you mean cutting them so they become 1.25" strips? First off, I think it would be very difficult to cut them straight. Secondly, they will make quite narrow finished strips -- which means more sewing, more cutting, more fabric, and a heavier finished top.
My recommendation would be to start out with 2" strips and use a June Tailor Shape Cut mat to cut them from yardage.