I've used Paslode framing nailers and they're pretty nice, but heavy. It wasn't mine and I don't know what the cost of the propane cylinders were, plus it seemed like we were always going for a fresh battery... I don't know, they're nice, but I wouldn't buy one.
Because of this, I like nailguns that work off of compressors because they are lighter and *simpler*.
I've put up the cheap pine privacy fencing with 3" deck screws and it holds well in strong winds, no re-hammering needed, but when I had some hammering to do on the slats I noticed that some of the screws had sheared /forums/images/graemlins/confused.gif. It must have been from the hammering because other sections were fine. Also, a year in the weather and you're lucky to be able to find the screws if they're countersunk and the wood swells a bit. You can find them, but it's not easy and after removing a section a few times to get my tractor into that area I replaced the screws with nails. It's just easier to take the section out and put back for me.
Give me an electric screwgun anyday if you are going to run a bunch of screws where more than a little torque is needed. All you need is one cord plugged into a generator. Or better yet, a welder/generator /forums/images/graemlins/laugh.gif. You'll need the cord anyway for all the batteries you'll have to keep recharging for a battery screwgun.
BUT, one thing about screws is they are harder to put in. You got one thumb with the board hooked on it. You got the rest of the fingers clamped around the post steadying it. You got the other hand holding the tool... It takes a bit of muscle to get the screw going (provided it doesn't fall out) and keep pressure so the board doesn't back away from the post a little bit when the screw gets in that far....
SO, for that reason, I like your first thoughts, a compressor and a nailgun. Maybe you can get an electric compressor that you can plug into a gas generator/welder that will meet your needs too, and be handier for anything closer to home.
Just my ramblin' thoughts.