Consider what you are planning to do with the gun before you purchase one. By that I do not mean the specific project, but the general use you plan for the tool.
I can best explain by describing my situation. I do a great deal of building, but Iím not in the trade. Iím a DIY, albeit maybe a little more serious than typical, and I was looking to increase productivity whilst still being recognized by my loved-ones as a family member. When I decided to purchase a gun, I knew I would use it much less than a professional builder. Duo-Fast, Senco, and the other top brands have great reputations for reliability and customer service, but at a price. That price did not factor well in my overall need. I chose Porter-Cable because it was half the price of the top models, and still had a good rating in various comparisons I found.
No-doubt there would be those who would argue my decision, but so far it has given me no trouble. Eventually, Iím sure, it will break, yet that leads me to another advantage I have over the professional. That is downtime. When the gun needs to be repaired, I can live without it. Probably not so with the tradesman. Last year I only went through about 40 pounds of nails. A professional surely would use that in a month or less.
Even before I decided on a model, I went to various job sites and interviewed builders. I was trying to get real opinions on models, plus get a feel for how often I would be using it. Most of them were adamant about renting a gun first for experience, because they come in different shapes and weights. You may have a preference, or decide you donít want one at all. They do save time, but they can be very dangerous. The one time you do not want to use a gun is when you are unsure on how to use it.
Beyond that, stick with a name brand and a common configuration. My Porter-Cable uses standard 22-degree nails, which seem to be the more common setup with many brands. I have had no trouble finding them locally, although I usually buy in bulk from the mail-order houses. Although a professional may burn out the gun in 2 years, I should get 5 to 7 years out of the gun before major repairs are necessary, and repair parts are easy to find. At $275.00, it was cheapest of the known brand names.
One last word on nails and guns: There is no one gun that will shoot common, finishing, and roofing, etc. all together. You would need a separate gun for each type. I choose one for common nails because that is what I do most. For roofing jobs, I often sub out the work, or I will rent a gun, ore the job is small enough for just a hammer. I am considering a finishing model next year. They do a nice job with molding without errant hammer marks.
This is just a description on what worked for me. If my livelihood depended on the performance of a tool, my decision might have been quite different.