We don't make any specific device recommendations since this really depends on individual need. There are a wide variety of devices at various price and quality points.
Generally, we recommend you avoid generic bottom-of-the-range devices since these are usually very cheap for a reason – namely, poor GPS, display and processing components. Mid-range devices from name-brand manufacturers such as Sony, Samsung, Apple, Motorola, HTC, LG, Asus etc. are usually reliable choices.
A suggested approach is to try a couple of your preferred phone/tablet devices for a few days in the field first. This way, if the device turns out to be troublesome or is poorly received by your staff, you have only spent money on a few of these devices. If the trial works out well and your staff likes the devices, then you know it’s a good fit and you should aim to standardize on that device if possible. You can then go ahead and buy those devices in bulk, which normally enables you to negotiate a discount with your supplier.
- Tablet Sizes:
Generally, we believe that 7" tablets are the best option for pure app usage since you have more screen space in the tablet form factor. The 7" are still quite light-weight and easy to carry compared to 10" tablets. - Phone Sizes:
If you need your staff to be able to make calls, etc., then a 4.5" or larger phone would be ideal. Larger screens make app use that little bit easier for people with "fat fingers" :)