The short answer is - It Depends.
Long Answer - What works for me, may not be what works for you.
eg: For me, I use Strava instead of GC due to my workflow
Outdoor rides
Garmin → Strava → Intervals (Outdoor PM is 1sided anyways)
Garmin → TrainingPeaks (TP - Free) [ I honestly only use it for the weekly (daily) TSS chart it has on the mobile app. Once I replicate that on BreakAway, taking the data from intervals, I’m likely ditching it altogether.]
Indoor Rides
Garmin->Strava->Intervals
Garmin → TP
BreakAway → Strava + Intervals (LR Balance / HRV / Elevation / Speed / Dist etc from BreakAway direct upload to both Strava and Intervals)
Both Strava and Intervals does the dup filtering. (and Garmin uploads to Strava gets filtered)
But if you’re using Strava, you might want to search the forums to see what item #1 beings (rate limited due to API Calls)
cheers.