I have about a $50-$100 loyalty premium for Delta, depending on the route as I find value in C+ seating, club access, and generally better treatment.
That said, if I was booking less than a week out my C+ selection would be greatly reduced so that portion of the value statement would be less. It would depend on seating options on the other carrier, Delta's seating options and then a judgement of whether the added cost of Delta is worth it