I use Asda as they seem to be the cheapest for the food we buy. I agree on the dates on meet and veg not being very long, but I buy in bulk for a month so you only pay for delivery once and that way I get it out the way once and for all, cause I really don't like having to make a list and figure out what we're going to buy, so I only have to do it once this way! And it also works out much cheaper for us as you can make better use of the offers like 3 for £10 etc. I put the meat in the freezer before it reaches the best before date so it stays fresh! I buy frozen veg and we buy our fruit fresh from a local shop.
Before we used to order online we would aim for about £50 a week, so £200 a month, I managed to get a months worth of food for £130 last week!! It's so much cheaper buying it all in bulk!
Also, Asda do the price guarantee, where they have to be 10% cheaper than other shops on the 'comparable items'. I got a voucher of £10 once because they weren't 10% cheaper.