I generally like the ocado app which is easy to use but I just wish it wouldn't add everything you ever buy to your favourites.
They have a good availabity of delivery slots and reliable, friendly drivers. Sometimes the bags are packed without logic or care meaning things can be damaged on arrival. Ocado have a very fair refund policy though when goods arrive damaged.
I have been with ocado for several years and don't feel tempted to try any other delivery service.