Server GIS - portals

[artjom872]

I would like to get opinions and experience about GIS servers. Lets assume that we need to host our data and use them internally as well as sell them to others.

"Everyone" is using ESRI ArcGIS Server. But there is also GeoServer and MapServer (these need other software to bridge the gap between ESRI). ESRI option is expensive but others lack GUI, ease of use and some functionality.

So:
- What would you suggest me to consider in choosing between options?
- How they compare (management, functionality, administration)?

Now there is ArcGIS Enterprise. So feature looks more like ArcGIS Pro together with Portal? As I understand than anyone connecting to Portal needs license (or only those that want to publish something)? Could you share your experience? How whole Portal experience compares to open source alternatives (GeoServer with GeoNode with OpenLayers)?

There is page at: https://gis.stackexchange.com/questions/100273/comparison-of-open-data-portal-solutions

Which country national cartography and topography agencies are using free or open source GIS software at the back end?

Could you share knowledge and experience of why should I choose to buy ArcGIS for Enterprise instead of using free alternatives?