Samurott is water, you know. Replacing it with an electric pokemon is...odd.
Still, G5 has a couple of options. The aforementioned pokeom Eelektross, Zebstrika, and Galvantula all have their strengths.
Eelektross has no weaknesses. No, really. Electricity is weak only to ground, but Eelektross has levitate. However, it is not a dual-type, so nothing can hit this for massive damage. Not without gravity at least. Combine this with awesome HP and Attack, along with passable Defense, and you have the best long-term G5 electric pokemon in the game.
Zebstrika starts strong, but never gets any better. Good versus water and flying, but horrible against heavy tank-like pokemon. Not anything more than a temporary solution.
Galvantula is my current choice in-game. It has the hidden benefit of bug and electric canceling the weaknesses to flying and ground, leaving it with only one or two defensive failures. Its main weakness is fire. Relatively fast as well as strong enough to get the job done, Galvantula is best placed in a party that has failed to get a bug pokemon already. Note about Galvantula though, make sure yours has Compoundeyes. Unnerve is horrible, while Compoundeyes is at least relatively useful.
If you like legendaries, there is always Zekrom, you know. Being a cover pokemon, I don't think much needs to be said.