I've never seen apocalypse now. I'll watch that when I'm finished watching the Mad Max trilogy (I want to be able to say "Bust a deal, face the wheel" without feeling guilty)
If FNG is chosen we'll probably have a platoon of three or four squads with other stuff (Weapons teams, etc.). Each squad will be led by a player-controlled NCO and there'll be an HQ unit with one player being the commander, who'll allocate forces to the various missions that crop up, including assigning the extra stuff.
Some pros and cons:
ATZ -
Pros:
-Every player will have plenty to do every excursion.
-Things aren't quite as complicated and there won't be as much bookkeeping (That only really matters for me, though)
-A bit more open. Unlike FNG, there isn't a clear line drawn between the good and the bad. Some survivor groups you come across will be amicable. Some will even join you. Others won't be so amicable and if you're not charismatic/tough enough, you can easily have a fight break out.
-Hot threesome action. Watch a skirmish with road warriors spiral out of control as zombies are attracted to the sound of gunfire. Do you withdraw, leaving them (And their valuable gear) to Mr. Zed or do you risk it all for the loot?
Cons:
Because it's simpler, it's a bit less varied as well. Unless I use my Hand of God GM powers to shake things up, things may get slightly boring depending on your playing preferences. See the pros though, and see the note at the end. It's hard to pick which game has more or less variation
This one only really applies to me, map generation rules for ATZ are a little ambiguous and I may have to spend a few extra minutes before a mission trying to figure out where the hell everything goes. That won't matter for you, though.
Not as many guns. This wouldn't normally be a problem but certain guns are objectively better than everything else. I won't spoil it by telling you what they are.
FNG:
Pros:
In some ways it's more varied. Small skirmishes can quickly escalate and there are a lot of different units and weapons.
More guns
Air/artillery support is fun, although some of the bigger bombs can clear most of the map and are risky to use.
Cons:
Depending on the missions assigned and how HQ assigns units, you may not have anything to do on a given month.
There's much more bookkeeping on my end, because the game's so detailed.
On variety:
It's hard to decide which game is more varied. They're both equally varied, but in different ways. All Things Zombie doesn't have as much stuff as FNG, but the few things it has interact in a lot of different ways. Throw unpredictable players in there and there's a lot of variation even if there aren't that many elements in play.
On the other hand, FNG doesn't have as much of that unpredictability, seeing as there's BLUFOR and OPFOR, and they don't interact in many more ways than shooting each other. FNG's variability is in the number of different mission types (ATZ has three, raid, escape, and pursuit, and in 90% of cases raid is the only one you voluntarily choose to do. Escape and Pursuit occur as a result of the events of other missions. FNG has six different missions and they're all standalone events) and the amount of hardware available. While most missions will start out simple, they can quickly escalate as the enemy calls in heavy reinforcements, including enemy armor.
Put simply, ATZ has a small number of elements that interact in a large number of ways. FNG has a large number of elements that interact in a small number of ways. Both of them have a lot of variability and replayability.
Also notable is that it's very possible to "win" FNG. If you survive twelve months you can go home. ATZ isn't like that. There's no home to go back to, and it'll be years before society can even think about trying to rebuild.
Edit: I removed my vote.