The choice between these two tools can be outlined by two fundamental questions:
- What tasks do you want to address with spatial data?
- Are you working with other products of ArcGIS platform (do you have ArcGIS Online account)?
What tasks do you want to address with spatial data?
Basically it is necessary to choose the right product based on what you want to do with your spatial data. To create heatmaps, visualize hotspots, perform spatial search, or use geocoding features, I would recommend using the ArcGIS Maps for Office, where this tool is really good.
However, if you want to import your data from Excel spreadsheet into the map (in the form of variable spatial features - points, lines, polygons, rectangles, hexagons); if you want to enrich your map layers with new data form Excel spreadsheets; if you want to export map data from shapefiles to Excel spreadsheets; if you want to update your Excel tables with data from map layers, I would suggest you to use the GIS.XL add-in.
When you compare both tools, you will find that the ArcGIS Maps for Office is more focused to presentation. Advanced tools for spatial analysis offer the ArcGIS platform in other products.
Conversely, GIS.XL add-in is focused on fast, simple and effective cooperation between the Excel spreadsheet and the map (GIS) interface. Its aim is to bring (in relatively simple tool) core - frequently used functions of GIS apps directly to Excel window. Add-in GIS.XL does not have to be the ultimate solution for spatial data, but rather the gateway between spreadsheets and maps.
Are you working with other products of ArcGIS platform (do you have ArcGIS Online account)?
If you work with other ArcGIS products, you probably have the ArcGIS Online account. In this case, ArcGIS Maps for Office is an effective extension of the ArcGIS platform to MS Office. If you want to visualize and share Excel data within the ArcGIS platform, the choice is clear.
If you do not work with other ArcGIS products, It’s a question of joining to ArcGIS Online subscription. In the case of the GIS.XL add-in, you are not bound to any platform, and you can use your results outside of the add-in in other applications. Your results can be saved in the form of map layers (Shape Files) or you can export them to several "spatial data" formats, e.g. KML (Google Earth), GeoJSON (web services) or WKT (databases).
These are the two basic questions I wanted to point out when choosing the right solution. But the final decision is up to you. If you have any question or comment, do not hesitate to contact me through a discussion or email.