My Porter Cable FR350 uses 22 degree nails. I think the common angles are 22 degrees for plastic collated (round head?) and 34 degrees for paper (clip head?) but may be wrong. However, Paslode, Senco, and Porter cable nails are readily available at most of the big box stores. Don't know about the building codes where you are, but some areas (particularly coastal, hurricane wind areas), require round head nails as opposed to clip head, so that may be a factor in your choice. Regardless, make sure you can get a good selection of "bullets" (i. e. nails) because building sheds, etc, will require both 3+" and 2" range nails.
Another factor is how easy it is to set the depth of the nail driven. Some models are a real pain, and altho you can lower air pressure for smaller nails, being able to easily reset the nailer's punch is a big advantage.
You do not want any gun that cannot be set to where you have to pull the trigger to fire the nail. Those that only auto-fire when pressed are not good for angled nail application (like toe nailing studs). Auto-fire is also more dangerous, but can be an advantage when doing sheathing. For the beginner, it also results in a lot of double nails until you get the hang of it (DAMHIKT)
JMTCW and I am no expert.
Go
PS. Although my Porter Cable does, and has done, a fine job for me as an occasional user (I have built a couple sheds, and walled in a car port), it sometimes does not have the punch needed for 16d nails into hard studs. I would have bought a Senco, but they did not have the round head model when I was in need.