I use Asda for basics and Ocado for the things Asda doesn't stock.
I've used Sainsbury's in the past (until they totally messed up, about 8 years ago, then offered truly crap 'misunderstand, deny everything and blame the customer' service, I told them they either resolve the issue properly or I'd never shop with them again, they failed to resolve it, then panicked and sent vouchers, apart from spending those I haven't shopped with them since).
Anyway, I've always set up my list by searching items, then I return to and amend the same list, so no browsing-related problems. Though, it does help occasionally, usually by visiting a shop, to realise what alternatives there are.
Asda's staff are consistently pleasant and friendly, unlike Sainsbury's grumpy sods (oh no I can't step onto your carpet because you might blame us if it gets dirty). Ocado's are lovely too and will carry everything into the kitchen. Ocado are better at having everything is stock (not surprising as it's a warehouse not one shop). Where both stock the same item, Ocado can be shockingly expensive - even items on offer can cost more than the same at Asda and, Asda do their 10% less price guarantee, which pays up almost every time.
Basically I think Asda do amazingly well, considering their low cost approach, somehow their staff are more motivated and friendly than they could be, while Ocado have nicer stuff and are as lovely as you'd expect, given what you're paying.