I love using strava and IFTTT for beeminder; the connection works so well it feels seemless to me. Also Strava has a really strong community, good routebuilding because of how they leverage the massive amount of fitness data they consume, and excellent support for sensors and performance metrics for stuff like heart rate, cadence, cycling power, running ground contact time, etc.
I started off using mapmyfitness as well but it just didn’t seem as easy to use or well-supported as strava to me so I switched.