May I ask the name and model of the bikes?
A 12-26 is much prefer over a 11-31, because for a 11-31,11-32,11-34 the gears are too far apart. You may feel as you are missing gears in between gears. It may be good if you are planing on doing hills or mountain riding, but for normal riding it won't be as good as like a 12-25, 12-26, 12-28 9/10 speed. Plus not very comfortable/good for the knees.