Always do your online shopping on mysupermarket.com, as they compare your trolley across the major 4. Asda is always cheaper for us. .They don't include Aldi or Lidl probably because you can't get everything there so agree with Pootles2010 on that score.
We have a code for 3,000 Nectar points with a £75 online shop with Sainsbos. Never shop with them normally, do Aldi weekly then Tesco/Asda once every 6-8 weeks.
With Xmas coming up (we have 12 people & 4 dogs for lunch!!) we know we will need to a biggish shop at one of the big supermarkets so is this deal worth it when Sainsbos are likely to be more expensive than Asda/Tesco?