I have used Sainsbury's, Asda and Tesco, and found them all really good, over the last seven or so years, but recently have found that I often have to call Asda because shopping is missing. They always refund the cost of it, but you need the food, don't you, so going out to get what's missing just defeats the object. I find Sainsburys is the best consistently, in my area - South West London - but have to go with Tesco more often as it's cheaper.