Strava feels like it was made for athletes. Its tracking is hands down the most accurate (although with any of these products there is going to be some error). Tracking activities is the focal point of the application. With some other apps it almost seems like an afterthought considering the number of bells and whistles. The app has clean and easy to use social features that mostly stay to the periphery. Strava also seems to avoid the battery sucking energy costs of some of the alternatives (although this just might be a personal observation).
Perhaps most importantly, it is a remarkably stable application at the time of writing (as a developer I know these things can change). I've used a few other tracking apps that freeze or force quit just when you need them most.