Difference in altitude

[Haldo]

Sometimes I upload my gpx files to some online service like IBP or Wikiloc and I always get a difference in the total elevation gain and loss.

Oruxmaps tells me that I made 1060 meters and IBP and wikiloc are both around 1250

I use the sonny's DEM files and I apply the altitude correction based on DEM files after i stop the recording of the track.

Which is the correct number?