Ferromagnetic materials make the magnet stronger than non-ferromagnetic materials like paper, wood, or air. A wider nail will make the magnet stronger. Making the nail longer will not make the magnet stronger, unless you also add more turns to the coil.
I believe- If there is more metal for the magnet to reach for, then the strength will grow but it may be harder to pick up off of a surface depending on the weight of the nail. If it is a light nail, it would be more efficient for a quick result in having the magnet to pick it up
