What's the best power upgrade for my 01' Audi TT 225?

For the best bang for the buck you may want to chip the ecu. Power numbers will differ based on chip make. use up some minutes at vwvortex.com in the Audi part to learn what chip is best for you.

I agree, a chip will increase increase and add fuel for a noticable differance for the least amount of money. you may be able to add a better flowing exhaust to help the turbos spool faster. The great thing about "chipped" Ecu is it may be ugraded afterward to take advantage off other upgrades.

software upgrade