Hello

Here's one for all the online grocery veterans out there: why provider do you go through, and why?

We're trying to set this up, and I'm trying to weigh up the various aspects, especially:
How easy/convenient is the interface?
Do they have all the products that you prefer to get?
What's the hit rate with being "out of stock" if you're shopping towards the end of the week?
How well do they do substitutions?
Which seems to be better value, and why?

Interested in your thoughts.