It's difficult to tell the difference between a Fino and Manzanilla in a blind tasting.
They are both made in the same way and taste similar although Manzanilla tends to have a true salty tang.
Fino is aged in cellars in Jerez whereas Manzanilla is aged in the bodegas of coastal town Sanlucar de Barrameda. The flor, the veil of yeast that forms on the surface of the wine grows more thickly in the cooler, more humid town of Sanlucar and is said to be responsible for the subtle differences in style between the two wines. It is also thought that the sea air contributes to the particularly salty tang in Manzanilla.