Overall Powerhouses:
* Tyranitar: This pseudo-legendary is a powerhouse with high Attack and Special Defense. It can learn powerful moves like Crunch, Earthquake, and Stone Edge, making it a great offensive threat.
* Garchomp: Another pseudo-legendary, Garchomp boasts incredible Speed and Attack, along with a powerful ability in Rough Skin. Its signature move, Outrage, can devastate opponents.
* Metagross: This Steel/Psychic type has high Attack and Special Attack, making it a versatile threat. It can learn both physical and special moves like Meteor Mash, Psychic, and Earthquake.
* Salamence: Another pseudo-legendary with high Attack and Speed, Salamence can learn powerful moves like Dragon Claw, Outrage, and Fire Blast. It can be a fearsome sweeper.
* Latias/Latios: These legendary dragons have high Special Attack and Speed. They can learn powerful moves like Draco Meteor, Psychic, and Thunder. They can also be very useful in battles against trainers with strong physical attackers.
Support & Utility:
* Blissey: Blissey has incredible HP and Special Defense, making it a fantastic wall. It can learn a variety of moves like Soft-Boiled, Heal Pulse, and Thunder Wave.
* Skarmory: This Steel/Flying type boasts high Defense and Special Defense. Its excellent typing makes it resistant to many common attacks, and it can learn moves like Spikes, Roost, and Whirlwind.
* Gengar: This Ghost/Poison type has high Special Attack and Speed. It can learn powerful moves like Shadow Ball, Thunderbolt, and Sludge Bomb. It can also be useful for Ghost-type coverage.
* Suicune: This legendary Water-type has high Special Defense and HP. It can learn a variety of moves like Hydro Pump, Ice Beam, and Surf. It can also be useful for its ability, Pressure, which can make trainers use more PP on their moves.
* Raikou: Another legendary Electric-type, Raikou has high Speed and Special Attack. It can learn powerful moves like Thunderbolt, Thunder, and Crunch. It can be a deadly sweeper.
Specific Strengths:
* Houndoom: A great Fire/Dark type with high Special Attack. It can learn powerful moves like Flamethrower, Dark Pulse, and Crunch.
* Heracross: This Bug/Fighting type boasts high Attack. It can learn powerful moves like Megahorn, Close Combat, and Brick Break.
* Espeon: A Psychic-type with high Special Attack and Speed. It can learn powerful moves like Psychic, Shadow Ball, and Dazzling Gleam.
* Ampharos: A powerful Electric-type with high Special Attack. It can learn powerful moves like Thunderbolt, Thunder, and Shadow Ball.
* Feraligatr: This Water-type boasts high Attack and Speed. It can learn powerful moves like Crunch, Ice Fang, and Waterfall.
Remember: This is just a starting point. The best Pokémon for you will depend on your personal preference and playstyle. Experiment with different teams and find what works best for you.
Important Notes:
* HeartGold features a limited National Dex, so you won't have access to all Pokémon.
* The game features a level cap for most of the game, making level-dependent moves less impactful.
* Consider type matchups and synergy when building your team.
* Don't neglect the importance of EVs and IVs for your Pokémon.
* Have fun!