The most popular fencing wires used are 3.15mm and 4.00mm
These are suitable for most applications and being relatively soft, are easy to use. For property owners, with limited fencing needs, soft fencing wires would be recommended.
High tensile fence wires are more economical than soft fence wires and have definite benefits where long strains and wider post spacings are possible. They do, though, require more accurate straining and are more difficult to handle, particularly tying knots.