If you give an upholsterer a pneumatic staple gun, they're going to need 2 pneumatic staple guns! If you can only have one though, make it a long nose. A long nose staple gun will make it easier to staple into deep carved details of your wood furniture projects, and it will also reach the tops of frames often made difficult by those god forsaken backs of chairs. I highly recommend BeA staplers.
I bought my first in 2015 and have still never had it fail on me. I just oil it regularly. Yo do not however have to invest in an expensive stapler to experience the benefits of a pneumatic experience. Harbor freight has great 2 in 1 options that are perfect for fledgling upholsterers. Uses BeA 71 staples.