The last few times I have bought oil from Eurocarparts when they have a 30% discount offer with free oil filter. They are doing a 25% off engine oil at the moment but even at that there Shell prices are better than Opie oils and you have free deilvery.
I use Opie for gearbox and diff oils usually.
I can get Millers oil from work as we use this in the trucks ,and I use this in the Mrs 2.7 CRD , also a very good oil.
I am old school and change the oil every 6 months or 3000 miles.