True love prompts sacrifices, if there were a sacrifice counter I would think Mandakini would top the chart :-) Manimekalai would come a close second along with Kundavai. Why I feel kundavai as a close pair with manimekalai was it is easy to express love when the love for both is evident and known, at that time, it takes a greater strength to sacrifice or control the emotion for the greater good. Kundavai did that to a very great extent in helping the cause of the empire. No doubt tht Raja Rajan would not have been so successful without his lieutenant.
Nandini's love is very confusing, atleast for me... Everytime I read PS I feel she truely loved some one - infact once I got an impression that she even loved the old general:-)
Another love (if not to be stated as just couple) to be considered, I would put Sembian Maa Devi's name into the loop just because of the sacricfices she gave in to.