Being a student, and therefore not having a car at Uni, Online shopping is the way forward. I'm an Asda shopper. Tesco I found had issues getting their veg out fresh... Often it would be like next day it goes off...
The shop itself is cheaper - as you track how much you spend and it's much easier to find the smart price stuff if you want it.
The getting to the supermarket works out cheaper - £3 delivery < bus fair.
It's much more convenient... Fill up a van with crap
It's much more lazy

You get to meet lovely people like Ahleckz
Also, I've had no issues buying frozen food or anything like that off of Asda... Must say though, the people that deliver to me must think I'm a right weirdo... End up ordering like 20 tins of mackerel, 5L of Passata, and 3kg of Pasta in some shops...
I have had a couple of issues where they haven't delivered the right item/missed an item, but it's relatively easy to just get them to refund it. Also have had very few substitutes, but when I have they're always better items.
kd