Archived comparison
Gneta is no longer an alternative to Garmin Connect.
The Gneta app has shut down, so a feature-by-feature sales comparison would be misleading. This page now points to the useful work that remains.
Garmin Connect remains the home for syncing and viewing data from Garmin devices. Gneta no longer connects to athlete accounts.
The short answer
If you need an active training platform, choose an active product. Gneta is now a free research and tools publication.
Why the app shut downStill useful