It absolutely has to be fully synthetic and approved to a VW spec.
A 5w-30 to VW spec 507.00 will probably be the best even if you are on fixed rather than variable service intervals. Other than that a 5w-40 to spec 502.00 will do if you are on fixed intervals.
I am currently running Fuchs Titan Pro C3 5w-30 which is a 507.00 spec oil. I was thinking a 5w-40 would be better for a 135k mile engine but that was what National Tyres suggested. I was pleasantly surprised by the lack of valve ticks etc. and I will buy it again. In this instance, they were right and I was wrong
I couldn't find a single 507.00 spec oil in Halfords. The best they had was 4.0 l of Castrol Edge 5w-40 which was 502.00/505.00 spec.