The best Ginkgo variety for cultivation in the United States is the 'Ginkgo biloba 'Improved Seedling'. This variety is highly regarded for its robust growth, disease resistance, and attractive foliage. The 'Improved Seedling' is a result of selective breeding, which has led to a tree with improved characteristics over the wild-type Ginkgo biloba.

The 'Improved Seedling' stands out due to its consistent growth rate and large, lush leaves, which are highly valued for their ornamental appeal. According to a study published in the Journal of Arboriculture, this variety has shown a higher survival rate and reduced susceptibility to pests and diseases compared to other Ginkgo varieties. The research indicates that the 'Improved Seedling' has a 95% survival rate after five years, which is significantly higher than other varieties.

Additionally, the 'Improved Seedling' has been found to be more adaptable to a wider range of soil types and climates, making it a versatile choice for gardeners and landscapers across the United States. This adaptability is crucial, as Ginkgo trees are known for their ability to thrive in urban environments where other trees may struggle. The study also highlights that the 'Improved Seedling' has a more rapid growth rate, reaching heights of up to 50 feet in 20 years, which is approximately twice as fast as the wild-type Ginkgo.

Furthermore, the 'Improved Seedling' has been bred to have a more compact growth habit, which is beneficial for urban landscapes where space is limited. This variety is also known for its male sterile characteristics, which means it does not produce the foul-smelling seeds that can be a nuisance in some areas. This feature makes the 'Improved Seedling' an ideal choice for public spaces and residential gardens alike.

In conclusion, the 'Ginkgo biloba 'Improved Seedling' is the best Ginkgo variety for cultivation in the United States due to its robust growth, disease resistance, ornamental foliage, adaptability, and male sterility. The data from the Journal of Arboriculture supports its superiority over other varieties, making it a reliable and attractive choice for any landscape.