The Geodude line is the best Ground type for a playthrough of HGSS. This is because it's one of the strongest answers to the first three Gyms and continues to be useful throughout the entire game. Trading is not a requirement either — the difference between Graveler and Golem is generally negligible. Learning both Magnitude and Earthquake via level-up make Geodude simple to train at any point.
Steelix is less convenient to obtain, and its viability is contingent on your ability to trade. If you can't, Onix is reasonably helpful against the first three Gyms but falls off after that. If you can, Steelix's raw bulk and excellent typing give it good matchups against most major opponents — provided you can look past its low Speed. Catching Steelix at Cliff Cave negates the need for trading, but at that point Steelix has already outlived its best matchups.
Nidoqueen and Nidoking fill mostly the same roles in-game. Both are available early and have diverse movepools, allowing you to tailor them to your team's needs. In particular, they perform reasonably against Clair and Lance if taught Ice Beam, two otherwise difficult battles. Nidoking is slightly better thanks to its higher Attack, but both are great options.
The other Ground type options generally arrive too late to be worth considering, as Johto's level curve makes the time commitment inefficient.
Pokemon HeartGold and SoulSilver In-Game Tier List (Smogon)
