I understand that tablets are large investment for any organization. With the advent of mobile data solutions it is even more critical to get the correct tablet for your needs. With this in mind here are some things to consider:
1) Most ArcGIS native mobile apps work on Android 4.0 or later, iOS 8 or later, and Windows 10 tablets. As we continue to produce new apps and increase their functionalities it is important to choose an operating platform compatable with the apps you plan to use. More information on system requirements can be found here: Esri Software | ArcGIS App for Smartphones and Tablets
2 ) Screen viewability is very important, but also important is screen size.
Accidentally got cut off mid-typing:
2 ) Screen viewability is very important, but also important is screen size. Most field personnel wear gloves or other protective gear that impedes their ability to interact with a tablet. It is important to choose a tablet/gloves(they make work gloves for use with tablets)/stylus solution that will work with your field personnel. This will need to be an internal discussion.
3) Storage size. Do you need to store a lot of custom apps or data on your device? For instance do you need to work disconnected and store maps/imagery/other data on your tablet? You would want to consider increasing storage capacity for these devices.
4) Will you get these devices a mobile data service or will you rely on wifi? Either way make sure to consider your options on connectivity and the device's ability to fit this need.
Hope this helps!