Im guessing your talking companies that will map the car to suit the turbo?
In my own opinion, there are only 2 tuners I would choose from.
I chose RS Tuning in Leeds, due to good feedback from others who went hybrid with them, and because Paul is based pretty local to where I am.
The other who I would consider is Jabbasport. They've been doing the hybrid diesel thing for a while now, and seem to deliver the goods.
Before they dissapeared, I would have considered Allards too, as they were pretty much top of the game when it came to diesel tuning.