Oh man I've used the chicken extensively, in all the ways mentioned.

Playing it in the last position is great especially in the equalizer rule. It keeps absorbing the sneak attacks shielding the range monsters.

In the equalizer rule it also extremely effective to play in the first position with a meele attack monster with reach or opportunity or sneak ability in the second position. This way while the chicken absorbs the attacks from the opposition, the second position meele attacker can continue to do the damage.

And I've also used it just one position before my first magic attack monster especially if the magic monster I'm using has the ability to slow down the opposition team or has tank heal. This puts me at an advantage for at least one extra round before the magic monster is taken out and this extra round has helped win so many battles I can't even begin to count!