Starter Pokémon have always been named as such by the fact that they are the Pokémon given to you at the start of the game. As such, the are four different sets of these starter Pokémon. Unlike Diamond, Pearl & Platinum however, Heart Gold & Soul Silver give you access to three out of these four possible sets of Pokémon. As such, you can only pick one of them in each set so you must choose wisely.

#152 Chikorita, #155 Cyndaquil & #158 Totodile - "Johto Starters"

The first batch of Starters to consider are the Johto Starters. These are the Pokémon you shall be obtaining first in the game. You get these right at the start of the game. The Johto Starters are unique in that they and their fully evolved forms do not adopt any secondary types making them the only "pure" starter Pokémon.

With these Pokémon, the choice you make impacts the various other aspects of the game. Specifically, the rival character, Silver, will steal one of the other Pokémon, the one with the type advantage over yours, and his team will be adjusted accordingly.

Chikorita Bayleef Meganium
Cyndaquil Quilava Typhlosion
Totodile Croconaw Feraligatr

#001 Bulbasaur, #004 Charmander & #007 Squirtle - "Kanto Starters"

The second batch of Starters you will find are the Pokémon whom trainers start with when they begin the journey in Kanto. In Heart Gold & Soul Silver, these Pokémon are obtained by visiting Professor Oak after you have obtained all 16 Badges and defeating Red. He will compliment you on your success and provide you one of these Pokémon. As with all starters, they will be at Level 5.

Bulbasaur Ivysaur Venusaur
Charmander Charmeleon Charizard
Squirtle Wartortle Blastoise

#252 Treecko, #255 Torchic & #258 Mudkip - "Hoenn Starters"

The third & final batch of Starters you will find are the Pokémon whom trainers start with when they begin the journey in Hoenn. In Heart Gold & Soul Silver, these Pokémon are obtained by visiting Steven Stone in Silph Co. in Saffron City after you have defeated Red. He will compliment you, ask you what colour stone you'd pick and then provide you one of these Pokémon based on the colour. As with all starters, they will be at Level 5.

Treecko Grovyle Sceptile
Torchic Combusken Blaziken
Mudkip Marshtomp Swampert