I've had a Porter Cable framing nailer for years, it's been great. Something about air guns which hasn't come up: there are 'clip head' (1/2 head) and 'full round' (self explanatory) nails. In many areas, clip heads won't meet code. That's why I got a full head. (insert favorite joke here 
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SVreX is right about SENCO nails, they are much better quality. Other brands I've tried have jammed repeatedly, it seems to be the paper collating tape that causes it. The SENCOs use some kind of waxy plastic that doesn't get stuck in the gun.
I used a 'no name' coil roofing nail gun that belongs to a friend, it was hit or miss. No matter how you set it, it would not repeat results; one nail might be dead on, the next too deep, the next 1/4" too high. That was aggravating, popping a nail in then having to hit it again to get it flush. If I buy one, it's going to be at least a Porter Cable.
