Generally, on empty flights, you could argue for the 3 x 3 x 3 layout.. but if the flight is full, there really isnt anything that would make the 3 x 3 x 3 more desirable.

3 x 3 x 3 Best for Small Families. 2 Prisoners
2 x 5 x 2 Best for Large Families & Couples. 1 Prisoner


On an empty flight, the 3 x 3 x 3 becomes significantly better... all the couples will have a free middle seat.

Emirates offers a 3 x 4 x 3 layot. The seats are very narrow, and very uncomfortable... im sure we can all agree that the worst layout award can go to Emirates.