I have always used well known branded oil in my engines Castrol, Mobil, Duckhams etc and swear by Castrol Magnatec or Mobil 1. My Honda Accord is approaching 100,000 miles (I bought it new) and i have always used Castrol Magnatec. I have refilled the MGF with Castrol Magnatec and will continue to use this. I have been paying £17.50 for a 4 litre container, either from Halfrauds when its on offer or Opie oils. I also used the correct Castrol oil in the gearbox on the F. It is also very important to carry out the oil changes at the reccomended time or mileage basis, whichever comes first.
I would never use Halfords own brand oil even if it was free!!