Honestly they all serve different purposes for me and have their benefits and drawbacks.

Asda - best offers on branded stuff, good pizza counter, fairly cheap, shit fruit and veg

Morissons - Best craft beer selection, best "fresh" counters, best fruit and veg, a bit expensive

Tesco - Best kids clothes, clubcard offers sometimes decent, best foreign food sections, a bit expensive, shit fruit and veg

Aldi / Lidl - Cheap, middle aisle is great fun, limited selection

I find Sainsbury's a bit pointless, it doesn't do anything as well as the others despite generally being more expensive. M&S and Waitrose serve a purpose if you want slightly fancier stuff.