Hi Can you save your workout data to both Garmin connect and Garmin Training Center simultaneously, or one after the other so that the data be on both platforms?
ANT Agent can be set to automatically upload the data to Garmin Connect. The files are stored on your computer when taken off the device and will be accessed when GTC fires up or you select Receive From Device.
For me, GC and GTC are there and not really used. I use SportTracks for looking over the data afterwards (pity it doesn't run natively on the Mac) and RunningFreeOnline for the web stuff