I can't really decide, each derby has it's own way...
I can't really make a big difference between the Athens and Istanbul derby's. Neither between Manure - Shitzens or Neverton and The Liver is Evil ( 1985 Trademark ). And really...nothing between Dinamo B.-Steaua B. , Levski-CSKA, Red Star-Partizan and even Dinamo Zagreb-Split ( even though the last is not in the same city and even metropolitan area ).
For me, in Romania, the biggest derby is UT Arad - Poli Timisoara and not Dinamo-Steaua. Simply because thats where tradition is. Arad and Timisoara are first cities in Romania where football came at the beginning of the century, the derby ( violent, bloody, burning alive etc ) is older then Dinamo and Steaua even though recently both clubs hardly exist though Timisoara has a new team ( FC Timisoara ) and UTA are in the 2nd Division. The rivalry represents the hate between the cities ( 50 km apart ) and ironically, both teams had great players that were born in the opposite city.