I've only tried Sainsburys. It seemed like a good idea once dd2 was born and the thought of shopping with two children filled me with dread.
But after a handful of deliveries I have gone back to trawling the aisles... trying to go every 3 weeks and alone. I begrudge how long it takes me. It's a whole morning out of a precious weekend.
Twice the delivery time did not tally with what we'd chosen and the only time they successfully delivered us the milk we chose, it was out of date. 8 pints of it.
I woudn't mind receiving alternatives if they were chosen by someone able to put some logical thought into it. Instead, they appear to be randomly chosen items perhaps based on shelf proximity or some matching keyword. I always reject the alternatives but it's a pain when at 7pm you've been expecting milk and you don't get any.
I just wondered what other people's experiences have been like. The Tesco thread above set me off thinking about this.