I have used both endomondo and Runkeeper, i think that Runkeeper is better, but thats a personal choice. You can program intervals easily and it talks to you and beeps at end of intervals, clearer than Endomondo. I find i cant understand what the voice on endomondo says!
+1 for runkeeper, if you have a smart phone. Its free and you can program intervals easily. you dont have to keep looking at it like a watch either as it talks to you and beeps at the end of intervals!