Hardwood floors are a perennial favorite, popular for centuries as both a functional and decorative flooring material. When installing a new floor, the hardness of the wood will indicate the ease of installation as well as the durability of the floor.
The Janka Number
A wood's Janka number is a basically a hardness rating--the higher the number, the harder the wood. Hardness is tested on solid wood--engineered woods and laminate woods use different substrates for the veneer, so the Janka scale does not apply.
White oak is a common flooring choice, with a Janka number of 1360, which is not very hard. The hardest wood on the scale is Lignum Vitae with a number of 4500, which is endangered and not a good choice.
However Brazilian walnut rates a respectable 3680 and is more widely available. Caribbean walnut, bamboo, North American maple and royal mahogany are common flooring choices, and all rate in the 1400s.
Importance of Hardness
Your flooring decision should not be based on the Janka scale, as the harder the wood, the more difficult the installation. Even the hardest wood will scratch and wear.
The only difference is that harder woods are less likely to dent. Choose a wood you like the look of and maintain it properly, and it will perform well.