There are a few things to understand about nails (or staples. For our purpose here, they're the same) and about nailers:
Pneumatic nailers use the power stored in compressed air to drive a piston, which in turn drives the staple or nail in an instant. Unless you desire an old-school look, such as putting cut nails directly into the face (which can be very beautiful) there is no discussion of nailers versus hand-driven nails.
PRO TIP! Some flooring cannot be nailed. Floating floors are just that, and they are designed to expand freely. Nailing a floor that is not designed for it will cause huge headaches and void any warranties. Some floors use adhesive. It is best to figure out your budget and get the best flooring you can afford.
Generally put, the thicker and harder the flooring, the lower the gauge of the stapler. You should use 20 gauge for engineered pieces, and around 15 gauge for thick solid hardwoods.
There are two kinds of nails, full pneumatic and assisted pneumatic.
Your stapler also will require a cleat for the bottom of the tool which positions it at the correct height to engage the tongue of the flooring. You'll probably rent your nailer, so be certain you have all you need at the rental counter, including this. If you buy a nailer, make sure the nailer is appropriate for the floor you're working on.
Expect to nail the first row by hand with finish nails, as staplers won't get you close enough to the wall. You'll nail both next to the wall and into the tongue edge.
Be aware of expansion gaps. This allows the wood in the room to expand and contract with changing weather. Solid woods require greater gaps than laminates, and you never want more gap than your baseboard will cover. Check with the manufacturer of your flooring to get a good number.