I can thoroughly recommend these guys. Andy, Alex and Tim are all complete VW enthusiasts who love their work. I'm going there two weeks today actually.
Some of the cars they work on there are absolutely mental! All sorts of top-end RS Audis, Porsche and VW are usually on site. They do a lot of supercharging of the 4.2 V8, and have worked on loads of TFSi & TSI engined cars. They have a 700bhp Mk1 Audi S3 with the 2.5 TTRS engine!
I had a PDT map on my old car which was done at Storm, and I still get to drive it. It's a fantastic map, delivering power smoothly yet progressively throughout the rev range. This car is wonderful to drive, and the map was only £300!
I then got my new car and had one of Storm's own maps on this one, and again the car felt superb to drive. However, when I went back for a free update they wanted to give me, the ECU had a hissy fit, and i had to go for a Revo map instead, which is also very good, if a little aggressive in comparison to the smooth delivery of the other 2. But this was £600, and if you don't need the switcheability between stock, anti-theft, and 3 different performance settings, Isn't really worth paying double in my opinion.
To start with, these guys can provide you with an excellent Stage 1 map for a really good price, and will then offer you advice on further upgrades based on what's best for you and your particular car rather than what's best for lining their pockets.