Bulbasaur is a Grass/Poison-type Pokémon and is the least popular. It will evolve into Ivysaur at level 16, later on to Venusaur at level 32. Bulbasaur and its evolutions are balanced in offense as well as defense.
It learns some useful moves in its early stage, such as Leech Seed at level 7, Vine Whip at level 9 and Sleep Powder at level 13. For Ivysaur, Razor Leaf will be learnt at level 20 and the powerful Double-edge at level 31. Upon evolving into Venusaur, it will learn its best Special move, Petal Dance, at level 32, Synthesis at level 45 and its best Physical move, Petal Blizzard, at level 50.
Bulbasaur holds a type advantage against the first 3 gym leaders, Brock, Misty and Lt Surge, as well as the last, Giovanni. This makes it a very good choice for beginners or players who are not planning to use most of the Pokémon found earlier in Kanto. Being one of the best Pokémon of either of its types, it also has the added advantage of evolving at a lower level into its final stage than either of the other starters.
A Fire-type Pokémon, Charmander is the most popular starter. It evolves into Charmeleon at level 16, and into Charizard at level 36, gaining a secondary Flying-type. Charmander and its evolutions are offensive Pokémon, focusing on Speed, Special Attack and Attack.
Charmander learns Ember at level 7, and the very useful Dragon Rage at level 16. Charmeleon will instead learn Fire Fang at level 28 and Flame Burst at level 32. Upon evolving into Charizard, it will learn Wing Attack right away, followed by the best Special Fire-type move it will ever get, the Flamethrower at level 47. Charizard can also get the very useful Flare Blitz and Air Slash from the Move Relearner.
This Pokémon only holds a type advantage against Erika. Despite being at a disadvantage in the early game, the move Dragon Rage makes up for it, allowing it to progress with ease. Fire-type Pokémon are incredibly difficult to find, with almost all but Slugma being classified as Very Rare. Having Charmander as a starter will mean that players do not have to worry about where to find a Fire-type Pokémon.
Useful moves such as Water Gun, Bubble and Bite can be learnt at level 7, 13 and 16 respectively. By evolving into Wartortle, it will learn Water Pulse at level 28, which should be replaced with HM03 – Surf as soon as you obtain it, and Aqua Tail at level 32. In its last evolution as Blastoise, Skull Bash will be learnt at level 39, as well as the powerful but inaccurate Hydro Pump at level 60. Blastoise can also learn Flash Cannon from the Move Relearner.
It holds a type advantage against Brock, Blaine and Giovanni, and the move Bite is very useful against Misty‘s Starmie. However, Kanto has plenty of good Water-type Pokémon, so it may be worth considering picking one of the other starters and catching many good alternatives later on in the game.