Have found both Asda & Tesco to be very poor but Asda much worse. Substitution & quality probs galore.
I switched to ocado with a £40 off first shop offer & pay £27 odd for unlimited mid week deliveries for a year; they price check everything & if it is cheaper elsewhere by a bit they send me a voucher. Recently I bought a lot of specific items for a hospice (think 20 each of 5 items)& it would have been a couple of £ cheaper at Tesco so they sent an apology & a £10 voucher!!
Also they do a thing when you checkout where you are offered overstocks at reduced price 10 items, & you can order as much as your freezer can take, 2 to 3 days pre delivery. Think half price leg of lamb or salmon or eg hovis wholemeal 800gm loaf at 60p or big bag of pedigree dry dog food.
Sometimes it's just getting shoot of seasonal stuff like Halloween Mr kiping, half price.
They almost never substitute & if you're not wedded to a particular brand, it's easy to order special offers & come out much cheaper than Tesco etc. I've only had a more expensive shop twice including hospice shop, & I do shop @ Asda & Tesco in store if I need a few bits, because I'd never ever get quality fruit & veg from them delivered.
Ocado on the other hand - if something gets a bit squashed by packing or don't look perfect, request a refund online & it's sorted. No sitting on the phone with bp rising or (asda) staff accusing you of lieing!
Finally, they make me very happy by sending me a choice of wines every year in my birthday month!
They do lots of other stuff that you can have delivered with your order - they have a pet store & a home store & a techy gadget store all on their website so more like an online department store, but with amazing service and no quibbling, just very can do.
Infinitely better than waitrose & far more variety eg French groceries; Swedish food; USA specialities; organic veg boxes, but apart from the waitrose essentials they undercut them often with their ocado brand stuff, which is a little hit and miss, but their completely open reviewing system works better even than amazon from my pov, as if somebody happened to be sent a free sample -yup, you often get free samples sent - & thought the sample was s**t, they can & do say so freely.
I have used Tesco asda waitrose sainsburys & ocado, especially with the multiple vouchers & free delivery pass you often get with eg Tesco over the last 13 years & I'm sticking with ocado now for the foreseeable. Can't be doing with hassle.