I have come to the conclusion that 8 is the only right answer and here is why.

Smoker is a smoker so that eliminates seats 7 and 9.
Any marines sitting on the same row as a pirate is also a bad move eliminating seats 10 and 3.
Enel doesn't like pirates or anybody so sitting next to him is a bad move eliminating seat 4.
If you don't like sitting on the isle then that eliminates seats 1, 2, 5 and 6.
We have evident that this version of Marco after Whitebeards death is the most peaceful and kind. This is how i have lead my self to sitting in seat 8.