Metal fence posts cost more initially than wood fence posts. Steel posts won't rot. They can also keep a wood fence from warping or falling during a windstorm. Metal supports don't have the maintenance and repair costs associated with wood.
The main difference between stainless steel and galvanized steel wire is the tensile strength. Given stainless steel is steel combined with chromium when the steel is in liquid molten state, this provides additional strength compared to galvanized wire composed of steel and a coating of zinc.
Low carbon steel wire has < 0.20% carbon content. This is a general purpose manufacturing wire suitable for a large range of applications. This type of material has good formability, will take moderate bending or flattening, and can be roll threaded.