The first nail gun I bought was a Senco brad nailer. It was great for a first gun and really opened my eyes to the possibilities it presented. Problem with it was it could only handle short brads.
I came across a pretty good deal on a Porter Cable brad nailer that could handle longer brads. It's easily twice the gun the Senco it. More features and better ballance. Adjustable depth and ease on clearing jams is really nice to have. I then bought a PC staple gun. Theres a real treat!
I use a Hilti Nail gun for framing. It's old, big, heavy and indestructable. It's built dozens of homes, dozens of remodels, a few sheds and one barn. It works every time and has never needed any attention.
Because it is so heavy, I'd love to buy something lighter, but as long as it keeps working, I'll keep using it.
One thing to remember is to oil your nail guns before using them every time. I also wear hearing protection with my Hilti. Not sure if other brands are as loud, but mine will cause serious hearing loss!