My activities are usually spot on Garmin Connect vs. Strava. Occasionally Strava will be 1/100 mile less.
Strava wants to motivate you to additional 70 yards or whatever that is!
In the past I often had a few more meters when uploading on Strava but in during the last weeks there was almost no difference - maybe a change with one of the latest firmware-updates.
Several threads in the Strava Support site regarding how Strava calculates distance.