No perfect courier exists.
Mistakes happen, and as for delivery slots, I think thats a luxury rather than a given. Anybody who spends any time on the road at all should understand that genuine delays do happen.
It can be very frustrating when stuff does not arrive as planned, especially if you have waited in. But it is what it is. For every one person that is let down, thousands of others are not. Lets be honest, with the logistics involved and the state of our road network, its pretty amazing anybody gets anything on time.
We have used nearly every courier available over the last 18 years, and they are all a much of a muchness IMO.