I've been ordering for our Trust (5 Schools)
The answer actually changes daily, depending on what they have in stock.
We have been unlucky enough to get some of the Tactus Geobooks, which I ordered as non secured from DFE. but then noticed the secured ones were DELLS, if you have the safeguarding and filtering software, you can remove the management from a DFE managed one anyway, you just have to ask them for the passwords.
When I get the go ahead to order, I look at the model of laptop available, and order what looks best, and what will survive - the Geobooks are awlful flimsy bits of kit avoid them at all costs - Very are flogging them for £180 a shot. The Dells are okay selling for £380 on the Dell site currently, and the HPs are fine.
We strip of the DFE management and do our own thing with them.
If you are a Google school, get the Chromebooks