RG58U. This cable is of the coax type and has an impedance of 50 Ohms, a stranded conductor and the insulation is non-contaminating. A stranded conductor is more flexible and less susceptible to breakage than a solid conductor. These features far outweigh the slight decrease in signal strength. Cheaper cable should not be used, as the quality of the screen is usually the first to suffer. Antennas can be made from a variety of materials.
Stainless steel is common, but difficulty in soldering can create problems for the home constructor.
Self adhesive copper foil, such as is used in staines glass work, is excellent for embedded antennas. It is easy to solder and form around contours if necessary and is available in various widths. Another material is the conductors, complete with the inner insulation, from out of a 2.5 mm grade mains cable. This type of antenna has been in use now for 2 years - hence thoroughly tested. Discard the outer sheath - usually grayish in color.