I have noticed GSF have gone a bit downhill as far as quality in the last few years so usually get everything direct from VW. Their prices are pretty good.
Mind you having said that I've just looked up last service bills and got Longlife plugs from VW @ £27 incl VAT and leads from GSF!! Part no 905-QHT-024, £15 incl VAT. Not sure which ones they are. By the price prob just standard.