Gen I: Brought 151 Pokemon starting with Bulbasaur ending with Mew
Gen II: Brought 100 Pokemon Starting with Chickorita ending with Celebi
Gen III: Brought 125 Pokemon Starting with Treecko ending with Deoxys
Gen IV: Brought 117 Pokemon Starting with Turtwig ending with Arceus
Gen V: Brought 156 Pokemon Starting with Snivy ending with Genesect
So Gen V brought the most Pokemon.
Notes: There are 649 Pokemon starting with Bulbasaur ending with Genesect. Mew was not originally supposed to be in the game but was a Pokemon that the designer secretly put in right before it was done, not even Nintendo new about it. Gen III and Gen V are the only generations where new Eeveelutions(Evolved forms of Eevee) were not released.