I've been using both Endomondo and Adidas sport tracking apps. Right now I think it is a tie, they are both great and fun to use. Endomondo recently updated their app which improved the useability while Adidas improved the launch speed of their app.
I like the Alpine Ski mode in Endomondo. I switch it on at the start of the day and trace out all the runs I get in.
What is everyone else using?