I use the Trolley app and write my shopping list by store according to the best prices. Waitrose is usually only the best price when something is on offer.
4 pints organic semi skimmed milk, £2.25 Morrisons, £2.40 Tesco and Sainsbury’s, £2.45 Waitrose. HP sauce, £3.30 Morrisons, £3.49 Tesco, £3.50 Waitrose. Seafood sauce own brand, 285g jar, M&S £1.30, Waitrose £1.50. Own brand paracetamol tablets, 35p or thereabouts nearly everywhere, Waitrose 75p. It all adds up. On the Waitrose app I look through the current offers of half price and 1/3 off, but they’re rarely things I buy.
Location is relevant though, I have Tesco, Aldi and M&S very close together 8 miles south, Morrison’s and Home Bargains close together but 12 miles north, Lidl and Asda 13 miles west, the big Sainsbury’s even further. Waitrose is my only reason to drive 7 miles east! Im retired and have the luxury of time to plan which stores to visit on my twice-weekly grocery shops (I hate buying groceries online).
Freshness of produce is rather store-specific, I think, and stock rotation can be sketchy in any of them.