Chikorita is a bit difficult to raise successfully due to its lack of offensive moves and
difficulty against the first few Gyms. It has good defensive stats and Meganium ends up
being a bit well-rounded (though underwhelming), emphasizing still on those defensive
stats.
Unfortunately Razor Leaf is going to have to get you by until Chikorita learns Magical
Leaf at level 20 (as a Bayleef), and that's about it for useful Grass-type moves. It can
still learn some other attacking moves, but you're going to be wanting to use your
Chikorita and its evolutions to inflict status on your opponent's Pokemon, to set up
things like Light Screen and Reflect (it can learn them both!), and to stay alive in the
fight. Petal Dance, which is learned by Meganium at level 32, is alright for attacking
with, but prevents you from switching and confuses you afterwards.
I personally do not recommend picking Chikorita unless you're looking for a challenge.
Newer players should stay away from it. Sorry, Chikorita.
Cyndaquil is a pretty solid choice and does well against the first few Gyms. It is very
swift with its high Speed, and it has really nice Sp. Atk to boot. It learns Smokescreen
at level 6 in HGSS, allowing it to debilitate your opponent's Pokemon by lowering their
accuracy, and it keeps it up by learning a lot of good attacking moves. Ember is learned
at level 10, Flame Wheel level 20 (as a Quilava), Lava Plume at level 35, and Flamethrower
at level 42 (as a Typhlosion).
Cyndaquil and its evolutions learn pretty much everything they need to learn in order to
fight just by leveling up. You can supplement your Cyndaquil by teaching it a variety of
TMs, like Focus Blast, Fire Blast, Rock Tomb, or Sunny Day.
I definitely recommend Cyndaquil to the newer players or the players that want an easier
ride through the game. You just need to make sure that you have a Pokemon that can deal
with annoying Rock-types and Water-types, because they're Cyndaquil's bane.
Totodile is an interesting Pokemon to use. It has a lot of Attack and Defense power, which
is very welcome early on, and it learns some fairly decent moves. Early on, it learns
Water Gun at level 6, then the rather useless Rage shortly afterward at level 8, followed
by Bite at 13 and Ice Fang at 21 (as a Croconaw). After that, it learns a lot of offensive
moves and moves that really help kick it into gear.
Aqua Tail, Super Power, and Crunch are just a few moves that it will learn later on as a
Feraligatr. It has an awesome amount of diversity compared to Cyndaquil and Chikorita,
learning a lot of different moves. It's a shame that it doesn't learn Aqua Tail or
Superpower until much later, but it can make up for it by learning plenty of other TM
moves.
It certainly has a lot more Attack than Sp. Atk, so Surf isn't quite as good, but it's
still alright and you'll likely appreciate it. Feraligatr makes a pretty awesome fighter
later on and is a bit more versatile than Typhlosion.