When I decided to purchase my nail guns I selected to go with one manufacturer and looked at Senco, Hitachi, Paslode and Porter Cable and for no good reason selected PC.
I just thought buying all the guns from one company would make life easier for spare parts and repairs. The framming nailer is round head and the only thing about it that I do not like is the weight. Not bad if you are driving a few nails, but after a day of pulling it around and the air hose I am a bit on the tired side. The new air cylinder guns are nice, cost a bit more, and I am not sure about the length of the use with a framming gun. I do have a finish nailer with air cylinder and really like it over having the hose and compressor inside running.
Pick a brand name and you should be okay! Check with the local suppliers for nails and see what is selling off the shelves. Around here most are using the round head nails.