It's different if there are two parents or just one. You also have to go by the length of the flight and how old your children are. Since I'm usually alone, we take a row. I just don't want to sit away from them or put a child alone with a stranger.

Luckily, we haven't run into 3-3-3 or 3-3 very often. On Southwest, we tried both ways, 3+1 and 2 window/center in two rows, one in front of the other.

Car seats also complicate things. The car seat has to go either by a window in a center seat in the center section. Again, we took a row, usually the center (since most are 4 across). On WN above, we had a car seat so that went by the window.

For families with two parents and at least two kids, it's recommended to take seats in front of one another. I found this better than being across the aisle too on WN. You can pass things from front to back and speak to each other more easily. The biggest advantage though, is if you can put your kicker (usually the younger/est child) behind a family member. For rear-facing car seats, you don't have to worry that the person in front wont be able to recline their seat and complain!

I was alone on WN but I did find that it worked well. I did put my older two next to a "stranger". Turned out, we had a couple, each on an aisle, occupying the third seat in each of our rows. They were very nice and good about getting up when any of us needed to.

Don't do this though if you think you'll be getting up a lot with a young baby/toddler on a long flight. You're seatmate might get annoyed.

Remember that on many aircraft, they'll have shorter rows towards the back. So if the arrangement isn't ideal for the number of your family, pull up the seat plan and see if there is a smaller row somewhere you might be able to snag.

Also, extra tip; we had a row of 5 and we were 4. I mistakenly put myself next to the stranger. Not recommended because I was more wiggly, dealing with the kids, than if I had put my oldest there. Luckily, he was a good sport and slept through it all. If your oldest is school aged, this might be a better idea! Put yourself in the next seat, so you know that it's okay with the stranger and your oldest and you're more "centered" to take care of any younger children.