I have a Sainsburys, Tescos and Waitrose nearish me so can't speak for other supermarkets (will also visit M&S on occasion). Waitrose is still a novelty after being surrounded by Tescos!
For example:
Waitrose - fresh herbs cut and banded together so the stalks all point downwards, so after I've used some I just pour a little bit of water in the packet and store the rest upright in the fridge. Whereas Tesco fresh herbs are all muddled up so if I wanted to store them stalk-down I'd need to take them out and align them a bit.
M&S - does skinless salmon fillets - all others seem to be boneless but skin-on and sometimes I want no skin (so I have to faff cutting it).
Tescos - the 'Finest' ham comes in a reclosable packet, that actually works. Otherwise I put opened ham in a ziplock bag.
M&S also do nice food that other places don't but I was more thinking about comparable items where one shop does something more practically.