A few years ago we tested a lot of different devices and then Ipad was the best equipment. Now we order Ipad mini 4G or Ipad 9.7" (2018) 4G and use Otterbox defender cases with utility series latch. We use 128 GB memory in order to sideload large basemaps.
As the Verge states "Apple’s bare minimum still beats everybody else".
https://www.theverge.com/2018/4/3/17188626/apple-ipad-review-pencil-processor-2018-education
Other people have good experiences with Android. One important thing is to minimize the number of models you are using - we had good experiences of Samsung Tablets and bad experiences from Sony Tablets.
Windows Tablets are Heavy, got short battery life and are expensive.
