Sandstorm is useful because it not only boosts Garchomp's evasion, it also helps to wear down your opponent's Pokémon.
Hone claws is useful because it raises attack and accuracy.
I'd give Garchomp sandstorm, then use a baton passer like Smeargle to pass on swords dance boosts rather than hone claws. It does sacrifice the boosted accuracy, but the 2x attack makes up for it. Garchomp will be able to evade more attacks while dishing out powerful attacks of its own.
Sandstorm makes the most sense. Battles will be over quickly with both sandstorm and earthquake/dragon rush battering your opponents.
Hope I helped!