Many of Pokemon popular in the early stage, such as Pidgeot and Gyarados, are weak against to Electric-type moves. Magneton can use Electric-type moves and has few weaknesses. Additionally, Magneton is easy to power up by Candy because Magnemite is easy to capture during night time
Since Psyduck is easy to catch, You can stock Candy for powering up easily. Additionally, Golduck is a Pokemon who can use Water- and Psychic-type moves effective against to Poison-type Pokemon such as Venusaur and Golbat.