My wife and I rode for 2 hours this morning. My speedo measured 21 miles while Strava said she rode 25 miles.

Measuring the distance on google maps put us at closer to 21 than 25.

I use an Android app called IPBike that reads ANT+ sensors (speed, cadence, heart rate) then allows you to upload the data to Strava. It uses the waypoint features of Strava (segments work, route map works) but uses the sensor data for speed, distance, cadence, heart rate, etc. You can also use it for directions as you ride. The user interface is a bit "clunky" but it works great. It does allow GPS only measurements, but I trust the sensors more than GPS.