Obviously the Steel type. They are resistant to 11 of the seventeen types. It is the most used pokemon type for a Physical and Special walls
Well normal types only have one weakness which is fighting. but have no strenghs on any type.
The Magnemite family I guess is the most resistant Pokemon, being resistant to Normal, Flying, Poison, Bug, Steel, Grass, and Electric. Also, when using Magnet Rise, are immune to Ground type moves, their only double-weakness.