We use a MAHA LPS 3000:
http://www.maha.de/cps/rde/xchg/SID-...eLocaleAttr=en
It's been upgraded over the years, with a better cooling system.
We integrated a water spray system, to keep turbo car temperatures constant, the software has been updated for OBD interfaces etc.
We also have a quite strict manitenance program, a MAHA technician comes every 3-4 months to test the system, check the precision etc.
We also clean the rollers as often as possible.
It's a "brake", or load cell dyno, good for up to 800 bhp, compatible with 4wd cars included viscous coupling etc (not problem at all testing Porsche turbos, Lambos, Audi Quattro, GTR etc).
It has showed to be very precise, both between different similar maha systems around the world and also from car to car.
The results are also very consistent at different times of the year, with the same car giving the same results in winter and summer.