IMO RS Tuning may EEK a little bit more power out from your car than say Revo as if you have a good engine and everything is tip top I don't think you could better a Custom Map.
Having said that and been to RS Tuning a map they had done for someone else Mk2 Cupra made about 5hp more than mine. OK for willy waving etc lol, but on a Track 5hp is nothing.
Now if you chose Revo alongside an SPS switch and use VCDS (if youv'e got it) then you should be able to achieve the same thing. Then on a plus side you would have switchability to std, Valet, Performance and Immobilsed for security.
I am in no way knocking Pauls ability to map a 2.0TFSI as I know it would be a good map, but for me the adjustability I get from Revo far outweighs any others available. It's a personal choice that can really only be answered by you.
You could get Revo loaded on by RS Tuning and optimsed on their rollers!!!