I'm undecided on the Cooper Discoverer STT Pro, they'll probably last for a while but having tried them on the front of mine with Yokohama Geolander on the back, I felt the front end was letting me down more than the back end on Sunday in the mud. Up to now though I've been happy with them, just not 100%
Yokohama Geolander MT+ is still my favourite but no longer seem to be available, hence I'm using Coopers on the front of mine after damaging a tyre at RHB as I couldn't get a replacement Geolander MT+
The Toyo Open Country MT seems to be flavour of the month and I think everyone that's tried them have liked them. Phil is running them on the Range Rover, that said, he couldn't get up that tiny little hill at Rothwell and kept muttering about ice in the bottom of the dip which nobody else had trouble with...
I believe Carl can get a good deal on the Toyo.