you don't need to cheat get great balls at the fuschia city pokemart.
Take a good or super rod and fish in Viridian, eventually you may find a Poliwag*. Throw great or ultra balls at it until you have it. *That's the correct spelling.
cheat
The only way I can suggest is to paralyze it and get its HP down to red and then just keep throwing ultra balls (its possible with great balls but quicker with ultra balls) at it. Of course you could use your master ball but you should save that for mewtwo.
You have to use Pokeballs, Great Balls, Ultra Ballsect.Many Pokemon can't be caught in Leaf Green, like Mew unless you go to an event, but all events for Leaf Green and Fire Red have ended.
Cinnabar island use a great rod.
If i were you i would choose a bulbasaur because it is great for new trainers.
Great Balls:fallabor town Net Balls:Mossdeep city.
My guess is that they are safari balls, from the safari zone or great marsh.
from girl i forgot which cave but it is near the beauty resort thingy
if you know where the birds are then great, but if you dont then youre dumb.you just carry around 100 ultra balls and go to work.the way i caught them was rapidly press the b button.
you cant get free pokeball's
no strongest. just depends on who has the type advantage in a battle. they're all great pokemon!