A person who is going to fly somewhere, in the near future, would want to do what, prior to flying? If the person at all cares about quality, safety - and any other things that would be part of what an airline can/cannot give a person - the person would like to research the airlines; prior to ordering a ticket; and, because no research was done, lose out things that the research could have indirectly provided.
One way of going about this research, is through checking out some airlines ratings. And, in doing this, it's obviously optimal to go with the ratings given by people who wasn't biased. So, let's do that - and look at what some customers thought. As you will see, this will be a lot about the actual airport's flown from/to, as the airline's stationed there (while the airplane is on the ground). As every airline's operational at the ground, take the ratings given as an evaluation of what the airline's doing on the airport.

Let's see the airlines ratings. One person finds this a brilliant one - at 5/5 stars. The person's giving praise to the check-in-speed - as it only took 5-min - and that many things could be shopped for, and eaten, inside. There wasn't a lot of queing in front of security. Also, the people who worked there, in large, were nice to talk to.
Another person, at least rating-wise, to the same degree likes the place. This person's used heathrow, before - and, judging by what he writes, it has become much better. Before, the staff-people were not too good to deal with, which he says is gone, and the security's speed has improved. This person's also appreciative of the abilities to go buy stuff; as the previous reviewer was. What this one mentions, that the other didn't, is that, nowadays, you don't have to go by bus to your gate (which used to be how things were, here). The plane landed earlier than it was supposed to, and no wait were to be had for the bags, when having arrived.
A lot of people are happy with Heathrow's capability, so let's look at a reviewsperson who isn't. This one gives 1/5 stars. This low rating - as often is the case with them - is due to an incident. What happened, to this particular individual, was that the queueing was way too long - he/she having to wait for over an hour for the bags, and for half an hour at another time.