I use the Nike+ and I am really happy with it. It counts down each K for you and you can select what ever playlist you want to use on your iPod. At the end of your workout it tells you how far you went, time and calories burned. I finally went out today and ran a 5k and it felt great, there is nothing like it. I don't have the iPhone but I have the Droid and I downloaded CardioTraining but I have not tried it yet and I am so comfortable with the Nike+ and I know it is reliable but I figured with the ice on the streets or if I have a heart attack from being out of shape it would be good to have my cell phone!