3rd Gen Which Pokémon is better?

I'm playing a Pokémon ruby hacked rom, where they are virtually unaltered, and I have a Squirtle, Mantine and Shellder and I want to know which is a better option for a team out of Blastoise, Mantine or Cloyster, BTW I also have a Feebas and Magikarp.

use blastoise or cloyster. blastoise has decent attacking stats and excellent mixed defenses while clamster has moves such as spikes, ice beam and explosion to take out any pokemon who doesn't resist it. beware of its low special defense though

gyara can't abuse his 125 attack that well in this game due to water-type attacks being special; milo is outclassed by blastoise and there are better flying-types out there than mantine.

Thanks, I'm gonna use the squirtle and evolve it then.