Just unlocked TrainingPeaks Premium - 'Form' very different from Strava

All my rides are synced between the two yet TrainingPeaks shows 18 form, and Strava shows -4 form. Both have the same FTP value and heart rate values. Free 30 day code going around which is why I tried it.

Any explanation for the discrepancy? Different algorithms? Which would be more accurate?

Strava Form is junk and is not tied to the FTP you had at the time of any workout. They apply it as an living value that affects past and present workouts, effectively making it a false and misleading feature.

Others can probably explain better, but the bottom line is that TP is the one to trust.