I suggest considering your needs (now and future) and matching the power of the application with your needs and willingness/desire to learn new programs. AGOL is indeed amazing and the desktop ESRI software adds a lot of power to analysis...the apps are good (collector, survey123). If you don't mind the learning curve then this is a solid option.
There are many other options too with lower barriers to entry: google maps, bing maps, Excel has built in native mapping capabilities (and some cool ways to animate time series maps) etc. While these are not as robust, the ease of entry is nice. You might want to experiment with these first to see how much you will be wanting to use this type of analysis before jumping in with a more powerful suite of tools (a tool is only worthwhile if you will use it). Also depends on how much "in field" data you want to collect vs how much will just be using existing spreadsheets or shelter data systems reports.
For the adventurous QGIS is an open source (aka FREE) program that is really good but again...expect a learning curve!
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