Although hardwood floors are sometimes installed with an adhesive or even as floating floors, most are secured to the subfloor with fasteners.
If you want to use a manual flooring nailer, you have one option: cleat nails. If you prefer pneumatic flooring nailers, you have your choice of a tool compatible with either cleats or staples. If you already own a nailer or stapler, you’ll probably want to stick with what you have. If you don’t, consider the differences between these fasteners in holding strength, tendency to split wood, and cost before you make a decision.
It’s also worth mentioning that even though the spacing recommendations for cleats and staples are similar, the two types shouldn’t be used on the same installation due to differences in holding strength and allowance for seasonal movement.