We're going on a trip next week with a family of 4 (girls aged 2 and 4) and have a segment on a 3-3 config plane. I opted for 3+1 for that segment. The other 3 segments are 2-3 config, so we did 2+2 for those. We've done 3+1 before and it worked well to give the more tired parent a break across the aisle. Also, 3+1 gives much easier aisle access, which is critical with a kid of potty-trained age, especially on a longer flight.

We're bringing one carseat on board and going to try out one of those RideSafer travel vests for the 4yo (I won it in a contest a few months ago) so we don't have to bring the booster seat.