What is the best electric Pokemon in ruby?

three pokemon could all be considered the "best", depending upon your definition.

Magneton- high special attack, very resistant to attacks (only ground is super effective)

Issues- lack of electric moves (you should use a tm), only available later in the game

Lanturn- mixed types make it resistant and versatile, good move set

Issues- only available later in the game

Manectric- very high speed, high special attack, good move set

Issues- weak in other terms, does not handle damage well.

Depending upon which of those is more important to you, choose accordingly.