Which orange hero is better in formation?

Look at their skills. The higher the range of their skills, the further back they can be. A person with 5 range can cast from your back row to their back row, however if you put one with 2 range in the back row they wouldn't be able to ever cast it on the enemy. If you have a 3 range skill in the back row and it hits two targets, you will only hit one target with it because it doesn't have the range to go 4 spots....from the back row to the enemy's middle row.

Simple answer - put shorter range (2) in front.