... Asda, Morrisons, Sainsbury & Tesco ... they're all "a bunch of toe-rags" in MY candid opinion. Tesco's "saving grace" is, of course, its Clubcard system ... plus it's nearest to me geographically; Sainsbury [I don't know about, 'cause there ain't a branch in Perth -yet - although they're reputed to be the most expensive of the 'Big 4']. Morrisons have regular weekly price cuts and Asda, no loyalty bonus ... but probably the cheapest.
So my advice IS - shop around!