Having travelled on DC-10s intercontinentally more than I care to remember in the past two years, I can tell you that often 18AB can be decent because on most flights they block 19-20AB as crew rest. When you board they will often be curtained off. Although this guarantees you no more legroom it does help ensure that there won't be annoying kids kicking your seatback or playing with the tray table all night long. Also it removes the guilt factor if you want to recline before they clear up dinner. The last few flights I've taken some nyquil before getting on the plane and by the time I finish dinner I'm falling asleep.

That being said, I have seen centre-section pax move to these seats after takeoff so they can sleep better, so you can't guarantee they'll be empty. But if people want to move there to sleep, chances are they won't be kids kicking your seat. And if they are, you can politely inform the FA that you picked 18AB so no one would be behind you, etc.

Check the seat map for your flight to see if 19-20AB are shown. If they're not, try out 18AB. If they are shown, whether empty or not, then I usually try for any ABHJ seat as far forward as possible.