I don't understand how this question at it's core is any different from a "What job should I take?" question, which as I understand it is verboten here.
*The new job (which I already accepted) is nice, pays more, and moves my career along.
The old job could be nicer, might be negotiated into paying as much, and might promise to move my career along.
Should I give them a discount and thus be able to choose the old company?*