It depends on you. 

 -  Do you want the ending where you want to wake up from the nightmare? Don't fight the penultimate boss, and accept his offer.
 -  Do you want the undeniably worst ending? Don't accept the penultimate boss's offer when you don't have three Umbilical Cords.
 - Do you want to see the nightmare to the very end? Don't accept the penultimate boss's offer when you have three Umbilical Cords. 

Personally I think the first ending is the best.