DSG is the much tougher unit, clutch packs handle 2+ with no issues, whereas the manual gearbox ones have been well known to give up on stage 1 if your the enthusiastic sort.
Put your money towards an Edition30 or Pirelli if you wanna step up from your ST.
This depends on your budget, if you have up to 11k for a well spec'd 30 or as low as 5K for a Normal GTi.
Happy hunting, and it's worth driving each of these cars to see which suits your driving style.
DSG will do it faster and better but I'm biased of course