If it is of minor importance to you where you are seated on board, you do not need to make a choice. The distribution takes place automatically and as much as possible, the airlines try to place passengers on the same booking next to each other.
If you want to make sure that you are seated right next to each other, you have the possibility to pre-book seats on board with most of the airlines that we are in partnership with. You just have to log in to your booking account on the website of the airline you are going to travel with. This is done by stating the airline's reference number.