My experience has been it's a toss up-- 3+1 is good for aisle access, but then both girls spend most of the flight leaning on Mommy... and somehow one is always asleep or in desperate Mommy mode so we never end up switching.

At least with 2+2 he is dealing with one while I deal with the other.

Of course, the 3+1 option does give you lots of guilt points to use during jet lag. ;-)

K.