I've used both tires and the Dunlop Direzza Sport Z1 StarSpec's are faster and they handle heat better than the Falken Azensis RT-615's.
Current prices for each tire:
Falken Azensis RT-615 - $106 from EdgeRacing.com
Dunlop Direzza Sport Z1 StarSpec - $123 from TireRack.com
The Falken's are a great tire, but I would get the Dunlop's again.