MOBIL 1
For performance cars like yours, you cant go wrong, I have put this in all my cars which include Skylines, Starlet GT`s, Glanzas and Volvo T5 and non turbo cars and I never had any problems with loss ( cheap oil is too thin and leaks via gaskets etc ) or overheating etc.
Ultimately its down to you, but I would seriously recommend paying that bit extra as it really does pay in the long term, and for all those who recommend valvoline, redline etc yes they are slightly better but more expensive and on a V reg Golf slight overkill....
And I would suggest replacing the filter and flushing before putting the new oil in, and the results should be smoother engine with less noise for many miles to come.
Before anyone gets on the wagon, its purely my opinion after having used this oil for over 25 years now....