I've used Ocado previously: bit expensive, and currently using Morrisons, who are ok, but some of the quality of the fresh stuff is a bit dire. Think rock hard 'ready to eat' avocados and squishy peppers. They also seem to give very short dated stuff.
I'm a bit wary of Asda, due to the way that I've heard they put a charge on your card before delivery and then bill you when delivering.
What are your experiences, please?