I use Strava. Whether it's best or not, depends upon what you want. I like Strava because it lets me compare my performance to myself on other days, and to other riders. I am almost always near the bottom in those comparisons. But it motivates me to improve. I don't know which phone you have, but I've been quite disappointed in the battery life of my Droid3 when the GPS is enabled. You may find, as I have, that getting a GPS cyclocomputer is worth consideration.