I think the most widely accepted one is Coggan's which is what is used by TrainingPeaks, and which my Garmin seems to track to. Strava uses a different algo that seems to track the same below threshold but disagrees by a lot above it. Golden Cheetah seems to agree with Strava; I use GC for its power curve chart because I assume that since it uses a more conservative formula the FTP/CP estimate is lowball.
My ego prefers TrainingPeaks
