Starter Pokémon

The starters in each Pokémon Game are all different depending on the region the game takes place in. Each set of starters has three of the following type of Pokémon: Fire, Grass, and Water.
The Grass-Type Pokémon of the starters is normally the most easy to raise, while the Water and Fire-Type are generally harder to raise. Fire being the most difficult. However, the Fire-Type will(most likely)end up being the strongest of your Pokémon if trained well.
The first set of starter Pokémon was for the Kanto region, these Pokémon are the most know among all of the Pokémon(along with Pikachu). These Pokémon are Bulbasaur, Squirtle, and Charmander.

Bulbasaur is the Grass-Type of the three and is the easiest to raise.
Squirtle is the Water-Type of the three and is a bit more difficult to raise.
Charmander is the Fire-Type of the three and is the hardest to raise.
These Pokémon are starters for the games; Red/Blue and FireRed/LeafGreen.

The next set of starters is for the Johto region, which is the region after Kanto. This region has an all new set of starters different from the Kanto starters.
These starters are as stated: Chikorita, Totodile, and Cyndaquil.
Chikorita is the Grass-Type of the three and is the easiest to raise.
Totodile is the Water-Type of the three and is more difficult to raise.
Cyndaquil is the Fire-Type of the three and is the hardest to raise.
These Pokémon are starters for the games; Gold, Silver, and Crystal.

And yet more games came out, meaning more starters. The newer set of starters is for the region of Honnen. These also vary from the starters in the previous regions.
These starters are as stated: Treecko, Mudkip, and Torchic.
Treecko is the Grass-Type of the three and is the easiest to raise.
Mudkip is the Water-Type of the three and is more difficult to raise.
Torchic is the Fire-Type of the three and is the hardest to raise.
These Pokémon are starters for the games; Ruby, Sapphire, and Emerald.

And for the very last set of starters to be released, these are from the Sinnoh region. These seem to be the most uniqué of all the starters.
These starters are as followed: Turtwig, Piplup, and Chimchar.
Turtwig is the Grass-Type of the three and is the easiest to raise.
Piplup is the Water-Type of the three and is harder to raise.
Chimchar is the Fire-Type of the three and is the hardest to raise.
These Pokémon are starters in the games Daimond and Pearl.

And that is all of the starters for the major games yet to be released.
Who knows, they might come out with more games and more Pokémon... but for now, lets keep with the ones we have.