There is no such thing as a "best pokemon". It depends on your standards, views and preferences. If you're referring to weaknesses, it would be Kingdra, as it has only one weakness, or Sableye if you will import it from R/S, because it has no weaknesses. Otherwise, it is all personal preference. No Pokemon will be able to beat everything in the game, which is why you need a good party instead of just one Pokemon.
the best bird Pokemon on leaf green is pidgeot
the best electric Pokemon in leaf green is zapdos. u get it in the power plant.
on a bike
You can get Pollywhirl in Pokemon Leaf Green in Virdian City.
The Pokemon you can get in fire red and not leaf green are Electabuzz and Scyther.
the best Pokemon are on 1 2 and 3 islandsb
you can't get mamoswine in Pokemon leaf green because it doesn't exist in leaf green
Use a master ball.
there is no Pokemon green leaf and Pokemon leaf green you can't only diamond pearl platinum heartgold soulsilver and maybe black and white
No only Fire Red and Leaf Green and trade it from Pokemon fire red and leaf green
behind the door is leaf green u enter the Pokemon leaf green world
try fire red and leaf green packs