What they share
Both are nature names drawn from trees. Both are two-syllable with soft sounds. Both have risen steeply over the last decade across the English-speaking world. Both pair well with traditional middle names.
Pick Hazel if…
Pick Hazel if you want the earthier, vintage-leaning option. Hazel is an Old English tree-and-colour name, and it carries warm, grandmother-generation associations that make it feel rooted.
Pick Willow if…
Pick Willow if you want the airier, more lyrical option. Willow has the movement of the tree itself and leans softer and more modern.
Hazel is the warmer classic; Willow is the lighter, more flowing pick. If you are building a nature-themed sibling set, they also work beautifully together.