When it comes to nailing down flooring, there are a few different types of nail guns you could use. The most common and popular type of nail gun for this job is the pneumatic nail gun, which uses compressed air to drive nails into the flooring. If you don't have access to an air compressor, you can also use a manual or electric nail gun.
Assuming you're using solid hardwood flooring boards, you'll want to look for a pneumatic nailer that can shoot 1-1/2 to 2 finishing nails. These will be just the right size for most hardwood boards. You'll also want to make sure your nail gun has enough power to drive the nails all the way into the subfloor without bending them.
If you're using engineered hardwood or laminate flooring planks, you'll want a different type of fastener altogether. Most of these floors are designed to be floated on top of the subfloor, so they shouldn't be attached with nails at all. Instead, look for a pneumatic stapler that uses staples specifically designed for floating floors. These will usually be 1/4 crown staples in lengths ranging from 1/2 to 1.
No matter what type of flooring you're using, always test your fastener in a scrap piece of wood before nailing it into your new floors! This will help ensure that everything is set up correctly and avoid any costly mistakes.